Sanity Check! Mecanum wheels...

[Steve_Alaniz]

If the "X" is on the bottom... the gripping vectors are facing each other so you are pushing in on two wheels and pulling apart on the other two. You have forces fighting each other and the rolling vectors don't really do anything.
If the "O" is on the bottom all the gripping forces are outward at 45 degrees angles (from the axles) and opposing forces are canceled out by the rolling vectors.
It's a lot easier to actually change the wheels and see the effect. I've actually done this with the practice bot and it leaves no doubt. You may be saying the same thing in different words since the key here is what's at 45 degrees to the axle.. the gripping vectors or the rolling vectors.

Steve