How to Make Box2D Collisions Accurate?

I'm working on a platform game using the Box2D physics, but the collisions are a bit inaccurate. This means that collisions are centered on the hotspot rather than on the whole thing, like how MMF2 would have done it. As hotspots tend to be in the center of objects, this leads to objects "phasing through" each other until they hit the hotspot at the center. Is there any way I can avoid this? I know there has to be SOME way to do it simply. This seems too big to just leave.

(Yes, the collision masks are boxes.)

Thanks in advance,
Ethan

Update: We figured out the problem, the object was too big. We shrank it and it worked.

This is still odd though. Why does the physics not work right if something is big?