Straight-arm inversions, like most aerial skills, are a delicate balance of strength and mobility. If you cannot lift your legs high enough, your legs are “heavier” in the inversion and your lats have to work harder. In addition, your scapula need to remain stable as the weight of your body moves from underneath your shoulders to on top of them.
Most commonly, people close the angle of the shoulders too early in the movement. The lats help stabilize the shoulders in a hang, but shouldn’t be working to push the body back until the legs clear a 90 degree angle.
An easy way to ingrain a delay of the push back is to co-time exhalation, curl of the pelvis, and shoulder depression.