predictability of mpg size when using 2 pass vbr

[davexnet]

Hello -
when I encode at 2 pass vbr using the ntscfilm template,
I get a final mpg that is too small (I'm trying to get as close
to 795mb to fill up the CD) I used the fitcd bitrate calc for this,
but the mpg I got was only 690 mb.

I used min=850, (padding on), avg=1318, max=2616 - audio=128kbps.


When I encoded the entire clip again a CBR 1318, sure enough,
the final mpg was 792MB - very close to ideal.

Any thoughts on this?

Thanks,
Dave