Hi marstc09 and welcome to cdfreaks.
In a word, no.
When you choose dvd9 as the "target size", you are in fact choosing a DL disc as the target, that's why it says 100%.
100% means no compression.
If you were to try to place a large file movie, say 8 GB or so, onto a SL disc and choose dvd9, the burn will fail. The default target size for a dvd5 = 4300MB(. You can increase this to about 4470 MB.)
Any movie file larger than this when dvd9 is chosen, will fail. Actually, the application should prompt you when the incorrect target is chosen.
Sorry for the short explanation, but I'm headed out the door.
Hope this helps.