The QLF table would ‘maybe’ be able to effectively treat T11-T12. Even that is a reach with how much a patient would be required to arch/flex their L/S. Since we treat the lumbar erectors and thoracic erectors differently, with internal & external slide respectively, it would be very difficult to generate enough tension on the QLF table for T/S erectors.
I generally treat T1-T3/4 in CTF position. If dropping the head doesn’t create enough tension, I have them round their shoulders a bit. Anything T4-T12 related, I treat in the seated position with external slide. I’ve found that making sure their hips extend first generates more tension from pulling the erectors tight earlier.
I’m sure Dr. Brady has a more concise answer, but I believe it’s mainly for tension production reasons.