Reguardless of the shaft dia. the digital (non contact)tach still gets one "hit" per rev, so the dia.  doesn't matter.
You can put the reflective tape on the shaft, hub, or even on the spinner blade. Any where you can hold the laser safely and the right distance from the tape. (distance matters)
Here is the one I've got.
John

 https://www.ebay.com/i/253735650382?chn=ps

Edit: I just looked at the website I posted and noticed the guy only got a 95% rating.....not good.
I didn't buy mine from him, but that is the brand. I noticed there are several cheaper than mine now and I'm almost sure they would be good.