FYI: Here's what Tag reports for my two test tracks. Note the inclusion of the "album artist" tag.
C:\Documents and Settings\Neil\My Documents\My Music\Flac\Various Artists\Album
Title>tag *.flac
Tag - Automatic Tag from filename
Copyright © 2002-2003 Case. Minor additions by Neil Popham, 2004-2007
Version 2.0.53b1, Compiled 2007-05-07
C:\Documents and Settings\Neil\My Documents\My Music\Flac\Various Artists\Album
Title\01 - Track 1 (Artist 1).flac
Format: FLAC
Details: 44100 Hz Stereo, 1025 kbps, playtime 04:03
Tag: FLAC
Title: Track 1
Artist: Artist 1
Album: Album Title
Year: 2006
Track: 01/02
Genre: Synthpop
Comment: XX
album artist=Various Artists
encoded-by=neil
encoding=Flac 1.2.1b -5 -f
C:\Documents and Settings\Neil\My Documents\My Music\Flac\Various Artists\Album
Title\02 - Track 2 (Artist 1).flac
Format: FLAC
Details: 44100 Hz Stereo, 756 kbps, playtime 02:29
Tag: FLAC
Title: Track 2
Artist: Artist 1
Album: Album Title
Year: 2006
Track: 02/02
Genre: Synthpop
Comment: XX
album artist=Various Artists
encoded-by=neil
encoding=Flac 1.2.1b -5 -f
@Akkurat: Yeah, I just thought --list was shorter to write!
Edit: OK, on testing, it seems that MP3Tag writes a BAND tag, as suspected:
C:\Documents and Settings\Neil\My Documents\My Music\Flac\Various Artists\Album
Title>tag *.flac
Tag - Automatic Tag from filename
Copyright © 2002-2003 Case. Minor additions by Neil Popham, 2004-2007
Version 2.0.53b1, Compiled 2007-05-07
C:\Documents and Settings\Neil\My Documents\My Music\Flac\Various Artists\Album
Title\01 - Track 1 (Artist 1).flac
Format: FLAC
Details: 44100 Hz Stereo, 1025 kbps, playtime 04:03
Tag: FLAC
Title: Track 1
Artist: Artist 1
Album: Album Title
Year: 2006
Track: 01/02
Genre: Synthpop
Comment: XX
album artist=Various Artists
encoded-by=neil
encoding=Flac 1.2.1b -5 -f
BAND=Various Artists
C:\Documents and Settings\Neil\My Documents\My Music\Flac\Various Artists\Album
Title\02 - Track 2 (Artist 1).flac
Format: FLAC
Details: 44100 Hz Stereo, 756 kbps, playtime 02:29
Tag: FLAC
Title: Track 2
Artist: Artist 1
Album: Album Title
Year: 2006
Track: 02/02
Genre: Synthpop
Comment: XX
album artist=Various Artists
encoded-by=neil
encoding=Flac 1.2.1b -5 -f
BAND=Various Artists
So, perhaps, if BAND is working for you, you could change the line to:
IF @various@==1 SET VA_tag=-T $qBAND=@VA@$q