Well I guess I should have done a bit more research before posting.
In the example I shared, I did gain more FOV than just the change in magnification, but now that I look at all the details, I went from a 40mm objective to a 42mm objective and that may have helped.
I just compared two VX-3 scopes, both with a 40mm objective, one with a 1" tube, and one with a 30mm tube. And guess what...you are right! There is difference in the advertised FOV.
I should have considered that some of my increase in FOV came from a larger objective lense vs the larger main tube.
Thanks for the kind correction.