It's not always solely a problem with the axle to axle- It's string angle in particular, and I've had bows with 31" A2A that had better string angle than some longer bows- it has as much to do with the size of the cams, where the string exits them and just how far the limbs are travelling at full draw. My AM35 and Admiral have roughly the same amount of string angle for example. My GT500 had less closed angle than the AM35

(edit-trying to remember my geometry teminology, unsuccessfully)