I am fighting similar problems with fastrack but your gaps seem pretty extreme. Can you post your track plan. The curved part of a o72 fastract switch with that 1 3/8 extension should match a 072 piece with a 1 3/8 so you may need to add a 1 3/8 on the opposite side of the track. As an example, I have a siding off one of my 072 curves and I had to add a 1 3/8 one curve in on the other end of the track so the width of the curves match.
I am not sure if I am explaining that correctly but your track plan would help us understand.