So after writing all that about my saddle fit? I ended up helping another boarder look at her (new, demo) Specialized that had been fitted this past weekend by a dealer. I learned a few things from this.
1. I'm no longer convinced my shoulder clearance is adequate, and I'd like to work on that.
2. I have not a clue how I'm going to work on that.
3. It's unclear to me whether the saddle should sit 1-2" behind the scapula.. or 1-2" over the scapula.
4. The shims the dealer had placed were at the bottom of the tree, not the top as I'd always mentally pictured them being. I assume they were to fill gaps & make the (wide) tree narrower for the (narrowish) horse.
5. Back to #3 - rep had the saddle fitted so that it worked well when over the scapula and avoiding the dip this horse has behind the withers. Not being accustomed to said dip, I slid the saddle as far back as it seemed to want to go - perhaps too far back for this horse? There are a lot of steep hills that I ride fairly regularly, and I have concerns that a saddle fitted for a static back on a flat surface might be more inclined to shift back to where it 'wants' to be on a hill. It did not occur to me to ask that when I was on the phone with the fitter trying to help troubleshoot, but I will bring it up if it gets mentioned again (especially as the other boarder wants to do casual trails).
6. Wide tree + narrowish horse.. had thin Specialized pad and 3/4" fitting pads. I feel like my 1" Woolback + 1" pads must somehow be wrong - but it's actually working reasonably well. It just feels like maybe I could do better for her.
7. Good thing about Specialized: very adjustable. Bad thing: very adjustable. Very easy to drive oneself crazy.