Have a look at the following MOD:
linky
It basically is a mod that will get you the logo's as XBMC (latest version) sees them. As XBMC now can do native media flagging you should be able to use that and no longer need to abuse your studio tags for that.
So for what to put in to the tag to get the correct logo to display (should you want to keep on abusing your studio tag), it should be rather simple. What you can do is have a look at the Include_mediaflags.xml which dictates which logo gets shown based on what is in the studio tag (of for the DVD/Bluray/HDDVD logo's the file name) you can add yor own rule there stating that if it sees xxx123 it should display a logo for codec 123zzz or in case it sees xxx456 it should display a logo for codec HNZ9089 etc.
As you can see the studio tag is a far from elegant solution and the native media flagging of XBMC is a far nicer fix to this problem, so please use that as you will likely need to do so in the near future (next XBMC/Aeon release)