Something's up because it fits like socks on a rooster! Did you tell Ames about it?
The seam on my tanks sits in the same relation to the uprising opening on the core.
Measured from inside of the L bracket.
^Swiped your picture. I effen hate win-10! My best guess: 13/16” on mine.
^Bracket wraps around the tank, about 3 3/4” depending on how you hold your mouth.
You know what kind of hater I am, so I'm trying to blame it on installer error, but no dice on that one because I don't see how to get it closer, at least not yet;) Is the core a repro?