Not really. A fixed percentage leaves no one happy. Of course, if there's no other option, we just have to make do.
Anyway, the problem for me isn't the percentage of the screen at which the image is reduced, but rather that the images are reduced way too much.
Like in the following example, both images are reduced much more than what I needed to fit my screen. In fact, the lower one, at 760x600 didn't even need to be reduced.
Edit: I reduced my resolution to 800x600, and now I understood that the board always reduces the images to whatever size fits an 800x600 screen. If that's the only way it can work, then I guess what I'm asking isn't feasible at all.