Hmmm those #s seem way too high in my opinion. I have found this:
https://tredwear.com/dealer-application/
to be very accurate.
Just plug in width mm (295) and Height % (40) and click on calculate - for any diameter (17, 18, 19 etc) a 295/40 tire your "usable" sidewall should be around 2.4"
For a sanity check since this is MUCH lower then what you guys are saying. Here's a pic of my old 305/45/18s w/1" tall glued on RWLs. If you plug in the 305 and 45 and calculate you will see it shows 3.15" Here's a close up:
If those letters are 1", I think 3.1" looks correct just eyeballing the pic and there's no way a 295/40 is going to be more than 2.5" of sidewall at the max.
-Joe