Maybe the different mill reacts a little differently to screen sizes.  I have a sample checked once or twice/year and have always been right at 650-700 microns with the 3/16" screen.

I'd hate going down to a 1/8" screen, I can only imagine what that would do to output ↓ and fuel use  ↑. 

I'm pretty sure it wouldn't fall down in the bins/feeders either, I've already got enough trouble with that during the summer humidity.