I’m new at this and a little slow but I think I’m getting it now
If I go with your first recommendation I would end up with a 1/4 “clearance
Your 2nd recommendation I would end up with a 1 ¾” clearance.
The current toilet is a St. Thomas Creations 6206 Marathon II 12” rough in toilet sitting on a 11” rough in with a 1” clearance. No wonder it was right up against the wall. I wish the builders could be a little more accurate on the rough INS. My toilet in the other bathroom is around 13 inches.