BOTTOM LINE...i just installed Kohlers..12" rough. @ 10 3/4" MINIMUM!!!! From the *1/2" thick BASEBOARD that was used the tank LID barely....i mean barley rested into placed...so i shouldnt need to explain that the tank is ON THE WALL....12" rough tank...10 3/4" is all you got....10 1/2" will NOT work..(maybe...maybe the 1/4 difference could ride depending on the brand of toilet, style of lid, etc.)
SOOOOO...an OFFSET FLANGE will move 1 1/2" away from the wall...so chip the finish floor (its not a lot) OR. catch it on the top off framing...but 10 3/4" with drywall..baseboards. TOTAL for a 12" tank.