I had a little over 13 inch rough in. I had a 14 inch Unifit adapter handy, but with careful measurement, I determined that the the 12 inch unifit could be positioned to not have any blockage on the Unifit output on the old 4-inch cast iron closet flange. I drilled new holes.
If you were to do something like that with a 14 inch Unifit, I think you could pretty much have a 1 inch gap behind the toilet, which would not look bad aesthetically. In the picture, you can see that the original slots intended for the closet bolt are not being used. The Vespin 2 toilet covers it all, but it could have any of the toilets that use the Unifit.
The screws on the left of the picture are the original closet bolts, and two deck screws were added to make sure things were nice and tight. They might have been unneeded, but I wanted to make sure. The fender washers are stainless steel.
It took a lot of time, especially being sure there would be no interference in the flow. I don't know if a pro could justify this, since it is not something that Toto recommends. But I am confident it is effective.