When using a 25X grain focuser, I can see the grain getting mushy around 2-2.5 stops down with all my enlarging lenses and I have a few.

I believe what you are seeing and what Ctein pointed out in Post Exposure is that the lens is becoming diffraction limited at that point and is an indication that perhaps the Schneider is indeed a better lens than the others you are testing. Ctein's chart shows that most lenses of 2.8 peak at about 2 stops down and lenses of 5.6 aperture are quite often peaking wide open to about 1 stop down.

I would think DF's advice of making a print is well taken and I would think there is nothing wrong with your lenses other than I would be wondering why the other lenses are sharp beyond their peak apertures.

-Fred