There are several reasons. First, the 30" may have actually been too long and you didn't realize it. Second, just the geometry of the bow itself could make it change. If a bowis more relfexed in geometry your DL may need to be a bit shorter than one that is DEflexed in geometry.

We need a photo that includes all of your draw arm, including your elbow, but it looks pretty good, as far as DL anyway.