Blueprint child set root custom collision


In my game, I have a blueprint used as a base for every enemies in the game (BaseEnemy).
I am aware that to have a correct collision system, the root component of the actor must be the main collision shape (otherwise, some collisions are not detected - in my case, enemies didn’t collide with the player if he doesn’t move).

My problem is that each enemy really have different shapes so I cannot use just one shape (sphere collision, for example) on all my enemies.
In blueprint, a DefaultSceneRoot is added if there is nothing. So, this component is created in my base class and will be the root in child classes so the collision system will not work.

I cannot set my base class in C++ for now.

Well, my question is : what can I do to make custom collision for enemies ?

Thank you.