5.1 FAAC vs. AOTUVb5: Confusion Over File Sizes Options

[wswartzendruber]

Encoding stereo FAAC and AOTUVb5 at Q115 and Q3 (respectively) produce the following file sizes for CDDA:

5527007 - jump.m4a
3399338 - jump.ogg

But when transcoding AC3 at the same settings with the same encoders, I get the following file sizes:

242213733 - audio_51.aac
246684898 - audio_51.ogg

I would think the resulting FAAC encode would be significantly larger than the AOTUVb5 encode.

Any ideas? I read here that Vorbis has been modified to efficiently handle multi channel encoding.