I hope you figure this out! I'll be really interested to hear what the Ansur people say.
To my eyes, it looks a bit like it's sitting too far forward??? (The second photo, with the pad, looks better to me...)
Stardust is built similarly to Gandalph -- not quite as high in the withers, but close. My saddle has just a bit more room under it than your pix show yours -- and I do, as I mentioned in a post before, place it a bit farther back than that.
Perhaps this is my lack of knowledge, but is not having sweat on the spine a mark of an ill-fitting saddle or simply less contact? My understanding of looking at sweat marks is that they can be indicators of both?? I was taught that even sweat marks on the sides of the saddle but not along the spine was normal -- to look for specific areas where the sweat is uneven, but that if it's the entire spine, evenly, that's not an issue...
Like Gandalph, Stardust is a bit roach backed -- a fairly prominent spine (worse when he's out of shape, but it never completely goes away).
For me, the decider about this saddle was his reaction to it -- he was adamant he hated every other saddle I put on him (I tried four or five) and has not hated this one...how is Gandalph responding to it? Is he a horse that will tell you if it's not comfortable?
(And what a cutie -- a fleabitten gray! Stardust is one, too...just love 'em...)
Good luck! And please, do, share what the Ansur people say in response to your photos -- that would be GREAT for me to hear, too!
"Ours is the portal of hope. Come as you are." -- Rumi www.imaginalinstitute.com