So others know, the Static Back position is lying flat on your back with your hips at 90 degrees and the legs knee bent at 90 degrees with the lower leg (calf) supported on a hassock or box.
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Not to be contentious -- take a look at what that position actually does. The Egoscue Method book and the web site both have: "This exercise creates horizontal load between shoulder and pelvis, which contributes to thoracic extension by engaging the stabilizers and flexors of the hip."

That sounds wonderful and implies moving the bones in the backward direction noted as needed by ABC™. The problems come when one actually notes what is occurring.

First, the flexion of the hips causes a reversal of the normal and needed lumbar lordosis. That reversal leads to reversal and FLEXION of the thoracic spine rather than the extension noted. Further, besides that being reversed and forcing the thoracic spine into flexion laying on your back forces the normally backward curving thoracic spine flat moving the bones FORWARD into FLEXION rather than extension as they say.

This is another one of those "good ideas" which do not do what someone says but the opposite.

The reason the audio explaining it on the web site ends stating that "...sometimes it can actually weaken you if you rely on it all the time." Is not the reason they state but the fact that it reverses all the normal and needed front-to-back curves of the spinal column leaving the body in a somewhat decompensated and precarious position at the end of the exercise.

Again, this is not because I say so or some "idea" or an opinion. This is just an objective physical observation of the position of the body anyone and everyone can make which is the opposite of what they are saying.

Be careful to make sure that what you are being told actually matches up with what is physically happening.

Again, this is not my opinion. Anyone can easily observe and experience doing this exercise that the thoracic spine (midback), which is normally supposed to curve backward, is pushed FORWARD by the floor reducing the normal and needed curve of the spinal column and causing adverse compensating changes in other parts of the spinal column and pelvis, which is the opposite of what they are saying in the written explanation.

It might feel good for some because it will temporarily reduce the amount of mechanical stress on one area by worsening the condition and forcing the stress to some other area. This gives the apparentcy an improvement however, it is not an improvement just a change and almost always for the worse. The end result will either be a return to the previous configuration with its attendant symptoms and or pains or a change to something worse mechanically which may result in immediate or later symptoms that are different.