I know that the PE is not yet mastered, but I wanted to post a video to see people's thoughts. I currently incorporate seated straddle raises in my morning limbering for a set of ten. With these I also try to forcefully bring my hips up higher once in the top position. I'm in the first block and intend to stay there until my hips finally succumb to my will of them being more flexible. If anyone has any other know-how I'm all ears; and yes, I have all the stretch series and do them weekly (but as is known, you can't do your stretch series and expect to come back next week and be superman, author unknown, lol). For the im, I feel comfortable with these I'm using 55lbs in the video -- I've been adding five lbs every two weeks (so since I do the 3-day split, I add five lbs every three weeks, unless one weight increment is excessively difficult -- then I wait). I know that the ultimate goal is to be at body weight, so until my hips catch up I'll keep working these.
you asserted the most important observation, that you're working on the hip hinge instead of craning your upper body to give the illusion of more ROM.