Froglander, no worries about starting a new thread - unless you want to - I think it is certainly relevant to the initial topic.
I switched browsers and can see your photos, but the videos don’t play except for in the preview screen (stupid Windows!) so I don’t know that I’m getting the whole picture, but I think I’m getting enough.
Two things. First, in the video where you are running your hand down the front part of the saddle, there’s a BIG gap there - it looks too wide. And secondly, it looks like the saddle is placed too far forward over his shoulder. What would it look like if you moved the saddle back?
You want to be able to slide your hand under there, but not so easily, if that makes sense. You want there to be contact, enough so that you have to sort of shimmy your hand in there, but not so much that when you do so it pinches.
Someone on the dressage forum just the other day asked a question about the Corrector Pad (Len Brown) - have you looked into those? If you go to the website your eyeballs may want to bleed because it is so horrible, but it might be worth giving him a call to see what his recommendations would be for a saddle that is too wide and moves forward. He has quite a shimming system that may be what would help you.
His theory on saddle fit is interesting in that he actually recommends a bit of bridging when fitting the standing horse, because once the horse moves his back will lift and fill in the gap area. This is the first person I’ve heard say this - everyone else says that the tree should follow the curve of the stationary horse (as in the link you provided on saddle fitting from Out West). I have to say, though, it does make some sense. When watching Mac move around throughout the day in the pasture, sometimes he looks like he has a dropped back, so to speak (if he’s standing on a hill, or standing with a hind leg cocked, for example), and then other times his back looks flatter (if his head is down and he’s grazing, or he’s just standing napping with his neck relaxed). Even when you fit a horse who is standing square, his abs aren’t necessarily engaged and his back position can change tremendously with just a movement of his head and neck.
I feel for you, I really do. I feel like I am relatively good at determining if an english saddle fits my horses or not - but a western one still leaves me scratching my head even though I think I’ve found what Mac likes.