12" is a good spot,
Most tanks are set up to be 3/4" to 1" away from the wall at that point.
You really don't want the tank touching the wall.
The Toto Dalton, would be much closer to the wall than the Cimarron.
The Dalton works better too.
The Toto Drake would be 1" from the wall.
Many people put wainscoating or tlle on the wall.
The little extra gives some insurance for when that happens.
Or when someone measures by mistake from the studs instead of from the finished wall.
Rough should be 12" from the finished wall to the center of the drain.