[Box2D] Specific Collision Points

To elaborate on the title, I want to get the 2 contact points of a collision between to fixtures and determine what to do with it.

Basically I have a Rock with 2 fixtures on it, 1 is a collision based fixture that collides with everything but entities, the other is a sensor that collides with only entities. When an entity is hit, the sprite is scaled down to make it look “squashed”.

Now the problem is, if the side of the Rock hits an entity, it squishes, when in reality I would want to ignore that as only a direct hit from the rock would kill the entity and squash it.

I was thinking of simply just making the fixture for colliding with entities smaller and focused on the points of the rock I would like an entity to be squashed upon collision. Which I might end up doing.

However, I want to try this way first, for the sake of knowledge.

Does anyone have any idea do this?