BPP Setting Ignored?

In the transcode tab there is a setting for BPP. When I set this at any of
the higher numbers (ie 0.50-1.00) I get a transcoded movie that is much
smaller than the estimate that dvd::rip gives me (usually the movie is
1.5-2.5G when it is estimated to be ~4G). When I probe the movie with
transcode or play it with mplayer, the BPP reported is much lower than what
I specified to dvd::rip (usually around 0.25).

I have tried xvid and ffmpeg (both mpeg4 and h264) and the result is the
same. I tried setting the bitrate manually, and I can see in the log that
the correct value gets passed to transcode, but still the BPP reported by
transcode and mplayer is way off.

Any ideas what the problem could be?

Thanks -- Matt