Is there a minimum length requirement (UPC) between a double fixture fitting and closet flanges used for back to back toilets. Another thread alluded to this. I need to use a 10" rough-in toilet on one side, which puts the length from centerline of toilet flange to centerline of DFF vent at about 12.5". The other toilet flange dimension is only about 14.5" as well.

Is this wrong? Thanks,

Hazel

P.S. - I posted this on the toilet thread but urgently need the answer so sorry for the duplication.