Here are videos of me doing the same positions, since you said videos are better. I found that it was painful to try and perform this movement with my right arm. Hollowing my lower back and keeping my shoulder on the ground was painful.
Video #1:
Video #2:
Off to do my HS workout and TBs since I haven't yet today. We'll see how that goes. Will check back later. Cheers.
Also, the straddle V-stretch Coach just posted to Facebook looks to be something I will incorporate with hip extension work.