I'll go with the "too much squeeze" idea, too. Of course, it's also important to get the suit properly distributed before and at the beginning of the dive, or no amount of air will help.
I generally do the "sumo squat", "aborted backflip", and "Picard maneuver" to get everything in order. The "sumo squat" is just like it sounds, and it gets the legs in place. The "aborted backflip" is hands up and over the head, basically slapping yourself between the shoulder blades (or as close as you're flexible enough to get) with a bit of backward arching of the back, which gets the arms and shoulders in position. The "Picard manuever" is just a tug at the hem of the jacket, which is necessary to set my telescoping torso correctly.
If I don't do the "stretches", I stand a good chance of having an uncomfortable dive. Too squeezed is still too squeezed, but unstretched is equally bad for me. (Then again, it's all based on your particular suit design, fit, and materials, so your methods may easily vary.)