Dear Alex
@nypaloto
The Imagehover Addon doesn't work for Mobile devices because it requires a 'hover' state & mobile devices tend not to have this because you navigate with touch.
I see what you mean about the Tablet and Phone widths being confusing, It may be they are there to ensure that if a browser reaches certain tablet and phone sizes Imagehover works correctly ( if viewed on a desktop ).
Have a great day Alex and best wishes ✨
Richard