@potterywoman My endo has said anything under 10 is low enough to not cause bone problems. She also says any cortisol test while on any level of prednisone is not reliable. It may be the best available but she says it is just not able to reflect what your body is doing vs. what the prednisone is contributing. That made sense to me. I wish you success in tapering down successfully. I would possibly alternate high/low dose for a week of two before moving to a lower dose to see if that eases the taper process for you. What works for you is the best approach.
My Rheumy says she has several patients they cannot get below 2mg prednisone.