You are sharing lots of information.  I really appreciate it.  

1.) I thought 90/90 split squat was a hip flexor mob? Kefu, can you flex your glute at all?  When I do clamshells I do feel it in my glutes.  I am asking because I feel like I may have anterior tilt considering that I am finding my quads seem to be always tight. And I am wondering because I think my glutes might be weak.  I am thinking that I can activate them, but they just may be weaker.

2.) To determine your external hip rotation — I am guessing you can’t pigeon pose?  Is a pigeon pose a good test to see external rotation limitation?

3.) Is there a way to do a supine single leg bridge without a ball?