A couple points quickly:
Re supine groin progressive, it's a completely different exercise than the one you tried. I had the same experience working from the book. Tried the one with one leg bent at 90 degrees on a chair, the other on the floor propped up to not point out. Felt nothing in it, no real change afterwards, maybe a little worse. Did the Progressive version at the clinic and it was VERY different. My hip flexors were so tight that they would not release with the leg all the way down, so the body just tensed up. It was too much elongation demand so it torqued my spine. Starting up high with the hip in flexion puts the psoas into an advantaged position to release, MUCH less of a release demand than with it on the floor. It gives a little, then you lower it a bit, gives a little more, etc...
The version you did, I'll put it this way: in the last year I've probably used it twice in my clinic. If that.
Re Foundation, yes, pay close attention to form. Like with our stuff, makes a huge difference.
Re your last two questions, that's where I think the Gokhale Method excels. Addresses those issues specifically. Re sitting at a computer, Pete's book "Pain Free at your PC" is very helpful, as well.
Volkl Organix V1 Pro
Pacific Gut 17 gauge mains at 54lbs/MSV Co-Focus 17L gauge crosses at 50lbs