Best way to compensate darker clips [due to resize against white bg] in Boris FX / Media100?

Hi, I find it really annoying that if I take a clip, and make it smaller, and surround it with white polygons, the smaller clip becomes a lot darker. Even though I haven't made any light adjustments.
Then if I apply filters to lighten the clip, I never seem to be able to get a light setting that all the clips in the sequence look good in.

Is there something I'm missing here?

Am using Boris FX 6 with Media100 7.5
I have a video clip in the top right quarter of the screen,
and white polygons in the bottom and left of the the screen.
the video clip looks and renders a lot darker than it would if it was occupying the full screen.
How can I prevent this darkening, or, since this is a fairly common problem when I resize video, do you guys know of the best filter settings to apply to compensate?