2D - Overlaying Colliders - MouseDown not detected

Hi there,

I got a background element with a boxcollider2d and a an object (boxcollider2d) overlaying that background element.

Now I tried to raycast the object to click and I tried it with OnMouseDown(). When I move the object to an area where no collider is in the back everything works like a charm.

So why am I getting the Object in the back instead of the object in the front?

I also tried to adjust the z-value and I tried to use different sorting layers...no chance... When I use two different collider (boxCollider2d for the background and circlecollider2d for the overlaying element) it also won't work.

Any idea?