Correct, most tapes come with two numbers on them. The first is usually the number that the tape can hold uncompressed. When the data is compressed they can theoretically hold twice that number. Thus most tapes are listed as 12/24 or 24/48 or even 100/200 depending on the tapes you buy. I don't know of any tapes that have ever gotten a complete 2:1 ratio of compression though. My guess is that yours are 12/24 and they are only compressing somewhere around 1:1.5. So you can either put in another tape or buy bigger ones. Or I could be completely wrong and it could be something with the software. But the tapes seem to be the most likely suspect to me.

GEL