A month or so ago, I was up to SL/PE2 trying to get to 4x48r. However, I asked someone to checked my form in ABH, and he believed I should go back to SL/PE1, because my legs were not enough. When I did go to a much higher leg height, my glutes cramped quite a bit.
In my opinion, one of the reasons that make ABH tough is that you have to fight against 2 common dysfunctions at the same time: a lack of thoracic mobility and inactive glutes. Even though I am able to get my thoracic spine and shoulder to the correct height, it was personally very challenging for me, then on top of that trying to get the legs to correct height, which was why I regressed back to SL/PE1 in the first place. My thoracic spine works very hard and sometimes I would even get DOMS for several days there.
So a week or two ago, I was reading this book, Anatomy of Hatha Yoga:
There was an section that talked about arch body holds, and it talked about 3 ABH progressions. The easiest is arms by side, the second is arms perpendicular, and the hardest is arms overhead. I've been trying out the arms by side version, and I find it much much easier. It allows me to focus on one thing at a time, which is getting my legs to the correct height yet my upper body doesn't have to work so hard to get into the correct thoracic position. In fact, I was able to maintain proper thoracic position without even feeling it on my thoracic spine!
I'm planning to work:
1. ABH arms by side
2. ABH arms perpendicular
3. then back to SL/PE1
This regression allows me to focus first on proper gluteal tension while at the same time gradually increase the difficulty of ABH on the thoracic spine.