can't export avi in Pro in higher res

[Matthew Max]

Why is Adobe Media Encoder ignoring my specs? I tell it to export at 1.5 kpbs and it give me about half of that.
I'm using older avi that I shot several years ago in the same project file I'm using for new footage (ACHDV). If I stretch the avi to fill the screen (about 295% the image size), I can export at higher res (as far as I can tell by the information displayed). If I stretch the avi to only 225%, I can't get it to export at 1.5. I get only about half of that. So I'm not getting a clearer final result.

I realize that I'm mixing file types, but this has not been a problem before.