Wrong File Size Video Output

[jsinfate]

I am using a DVD5 (4.19GB) ISO file to convert to MP4 for my testing.

I just did another test using the Apple Theater Pro Res Default settings and the MP4 file came out to 4.8GB. I used all default settings and a single pass.
I even converted it to a single VOB file to compare and the VOB was 3.5GB.