Along with this posture, I find that figuring out where my shoulders go is a challenge. This is related to my previous question about shoulder position.
I try to keep my shoulders down (toward pelvis, not scrunched up), but that seems to require that I bend my elbows. If I do that, there is a constant interplay between activating my abdominals and my shoulders coming off the mat as an offset. I assume this is normal and part of the challenge of the pose? What you referred to as “proper way to use the abdominal muscles in harmony with the lower back”.
Thanks
hunter