To me it would seem like the perfect place to use imagepoints..
Depending on top hit or kick-leg or whatever, but if you want to know the overlapping area, it can be done.
I'm assuming the hitboxes are square/rectangular
Create 4 variables ValueYtop,ValueYbottom,ValueXleft,ValueXright
If hitbox1 is overlapping hitbox2
- Hitbox1.BBoxTop > Hitbox2.BBoxTop > ValueYtop = Hitbox2.BBoxTop
- else > ValueYtop = Hitbox1.BBoxTop
By comparing the boundingbox left, right and bottom you now get the 4 values of the top(Y), bottom(Y), left(X) and right(X) of the overlapping area.