Layer masking / PIP

Hey folks,

I was doing a show a few months back blending 3 DL2's across a hard set with two 9 x 12 screens built into the set. I wanted to mask out the 9 x 12's with black so I brought layer 2 to full and made a black box, as soon as I went to scale it I got a lot of distortion from my main layer (or bleed through) I also noticed this is the case with the Axons as well. I know there is a mask channel, but it only alows to mask in the center of the image. Is this problem going to be fixed, or is there another way to basically PIP out( or mask) a black box?? Thanks,

Geoffrey Platt
Lighting and Set Designer
www.plattlighting.com