According to Moens own specs, they allow 1-1/4" tolerance plus or minus.

If you found someone at Moen that doesn't agree with their engineered specs, then either that one person is wrong, or they need to change the spec sheet.

However, that being said, everything about that valve is working and I've seen many installed that way and in use.

A note to Chel,
Why did you plumb with galvanized pipe?
Combining galvanized and copper is never a good idea.