Mask on Auto Reframe

I have an high-res image. I put it on the timeline. The timeline is configured for HD. To have a nice framed image, I apply the Auto Reframe effect. That works. Now I want a Mask on the (resized/reframed) image, to see through that resized/reframed image and disclose what is underneath.

When I try to do that, I notice that the Mask that I make (I follow the form of the reframed object) is actually being applied on the original sized image, and thus reframed to a much smaller opace mask. The result is a totally different look-through than the drawn mask.

So how should I do this? How to apply this mask on the result of the (reframe) effect, and not the source?