Just push it on the horn of the bowl
It should be fine.
I just purchased my first Toto after reviewing information on this site. I expected the horn to be fairly round, but the one on this unit is narrower front to back. It looks as if the forward edge is pushed back. The open is 2" front to back, and 2.25" side to side.
Pic is attached with dimensions drawn.
Is this acceptable?
I am planning to use a Fluidmaster wax-free, and am wondering if the shape will cause a problem for the rubber seal.