in my experience vec_for_min and vec_for_max don't give back changed min and max values, eg. when you have deformed an entities and therefore changed it's dimensions. They always return the original min and max values of the entity. Could you implement that the functions always return the actual dimensions of the entity?
We'll implement a function for this in a future version. At the moment, you can do it with some DirectX commands. Open the mesh, retrieve the vertex buffer, and then calculate the maximum and minimum of the vertex positions. Y and Z must be swapped.