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| All in all, I'm guessing there'd be a few factors into play to consider.
With a bit higher boom height, it can make a twin fan/angled nozzle suck for getting into the canopy. Not the biggest deal on wheat fungicide, as you are generally targeting the front and the back of the head ONLY (or at most flag leaf and up), so penetration is less of a concern. With a shallow angle nozzle up front, the spray can start travelling/rolling horizontally which works really well for wheat fungicide.
When it comes to canopy crops that you are trying to cover more than just the top of the canopy, you'd be better off spraying straight down, or at the very least spraying angled with a coarser spray than you'd think. Again, the angle of the nozzle makes a big difference. Even a 45° to a 60° makes a big difference if you are spraying pretty darn fine spray. Consider, at a 20" boom height off target, if you are spraying straight down, you are only spraying 20" down. (Not really a trick question). The tough thing is that different sized droplets can travel a difference distance before they are effectively checked out. (Can't go any further without gravity, sprayer speed turbulence, wind speed, etc.). Even the bulk of the 'really good' droplets that'd be like medium spray can really only spray like 14-16" before she stops dead.
What's that mean for straight down spraying on 20" boom height? Probably not a big deal at all as you are pretty much right where it needs to be.
But what happens with an angled nozzle? The spray droplets of those sizes are still going to only go the same distance (just because they are sprayed at an angle doesn't really mean they can magically go further), so you are going to end up with less canopy penetration and more chem hung up in the top of the canopy. Again, for something like the green leaf nozzle, it isn't really ALL angled spray, so the 'bad stuff' about the angled orientation would be lessened.
I had put together a bit of a theoretical layout for angled nozzles, as well as a simplified image with a normal enough 20" boom height with a 30/45/60. Again, this is ROUGH and was more for my own use, but it'd give a decent enough representation of what might be going on to the point in that Beck's page showing the green leaf beating out a twinjet in the same application by such a margin.
The twinjet is a wider angled twin tip, and produces WAY finer spray than the green leaf. With the extra angle (meaning extra distance to target) with droplets that are too fine to be able to get into the canopy consistently, you are worked into a corner that you'd only do a solid job if you are spraying like 15" off of the canopy or lower (which isn't feasible).
In a nutshell, a few things to consider when spraying (sometimes in general, but more emphasis when you are considering crop adapted spraying (adapting how you are spraying to better target a crop)
1. Stand in the crop. Look down. Visualize if you can spray where you are targeting for that specific application with where you are. (e.g. are you even able to see the weeds in the canopy, or try to visualize painting the FRONT and the BACK of a head of wheat from the ABOVE view.) This might give insight into where you require your coverage and see if there is anything you can do to help.
1a. Sometimes the only options are to increase water volume, but often for the high volume applications into canopy crops that require a high level of coverage, remember that by going to a larger nozzle, you are naturally going to be producing coarser and coarser sprays by doing so.
1b. Keep in mind that coarser droplets will generally get hung in the top of a canopy. They will NOT provide coverage into the mid-lower canopy by running down the plant. It doesn't really work this way. So, if you are spraying a contact-based application, you will require those smaller droplets to get into the canopy and have a chance at good coverage. If you are spraying 20GPA at anything 14MPH+ (ESPECIALLY if you are using a PWM system), you'd likely start benefiting by splitting up a flow rate into two more meaningful spray nozzles. This can be in a variety of ways (e.g. if you have access to 10" spacing, double-down adapters/nozzles, spraying with stacked nozzle bodies on 20" spacing, using angled nozzles if you dont have access to any other means of double-down type spraying setups)
2. Even though having the 'fine mist' spraying into the crop looks pleasing for those applications that aren't really as drift sensitive (e.g. fungicides), but consider there is a cost to missing application both in application cost (fungicide is expensive), but also much of that application might have the means to evaporate before its effectively done what it means to do. Fungicide is often a tough gauge on efficacy as well for many applications as they are labeled for suppression, so even if you achieve a perfect 100% coverage, it doesn't mean you will have 0 disease presence. All in all, try mitigate driftable fines to a reasonable level, then concentrate on coverage. Easier said than done, but use what you can for info.
All in all:
I've seen solid benefit using angled nozzles with wheat fungicide with cereal or vertical growing crops that do not require penetration into the canopy. (e.g. Spraying for Fusarium Headblight in wheat - paint the front/back of the head only, with ideal coverage only hitting flag leaf and up)
I've seen solid benefit using more than one nozzle straight down with canopy applications of fungicide, desiccant (or defoliant), or high volume herbicides that require solid coverage in a complex canopy. (e.g. spraying Canola fungicide for sclerotinia in a thick canopy, spraying glufosinate to better kill complex weeds in-crop at high volumes (15GPA+), or 15-20GPA+ rates of reglone/dessicant in peas/lentils/pulses/etc.)
I've seen solid benefit using nozzles adapted to be inside the canopy, oriented toward the tassle in corn applications of fungicide. (e.g. drop hoses into canopy and have adjustable nozzles spraying to the side of the canopy, instead of straight down)
Anyways, a fair bit of info there, but hopefully you find some of it to be helpful. When considering angled spraying, If I was using angled nozzles, I'd tend to sway towards being a bit coarser than you'd prefer spraying straight down to help the spray get down into the target area better before it shears off in the wind/sprayer speed/etc.
Let me know if you want any clarity on any of that info.
 (Spray Angle Distance (full).jpg)
 (Multi_Angle_nozzle Breakdown (full).jpg)
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 Spray Angle Distance (full).jpg (42KB - 185 downloads)
Multi_Angle_nozzle Breakdown (full).jpg (34KB - 176 downloads)
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Nozzle for fungicide
