I see Tom's not on right now so I'll give you my experience. The biggest diameter waste "tube" I've found in a toilet is 2 inches.
In other words, the best toilet I've found can flush a 2" ball.
...so if the diameter of the 2 finger flange is more than 2" then it's probably bigger than the waste passage through your toilet...so you should be just fine.
Does that make sense?
[Do, though, give it another day. Our resident plumbing expert will set you straight fer sherr

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