yeah, you can probably tell by the iso size. xgd2 games, iirc, are 7.05 or 7.29GBs regardless of the actual game size, due to padding and security sectors. xgd3 games are probably larger, and likely have a set size for all of them as well.
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another possibility is the layer break causing a problem. that's what the .dvd file is for. you don't need it if you set the layer break in imgburn by default for dvd-9. however, I'm sure the layer break for xgd3 games is different than xgd2 games, which was like 1,931,760 or something like that off hand memory. it's close to that, but you can check in the .dvd file as it will specify the layer break. that's the file's entire purpose.