Regarding placement...
Can't tell for sure but it ~might~ be a little too far forward. You want the front of the saddle no further forward than the point of his shoulderblade and it looks like the saddle might be on it.
I would, to seek placement for his back and his movement, put it on him snug but not tight, and either ride or lunge him at the trot, on level ground without the breastcollar on. His shoulder movement will move it back to where it comfortably wants to be. Then fit the breastcollar.
That's if it otherwise fits... of course.
Well, I'm heading to bed. I can't think about this anymore.
Thanks for the advise. I'f they don't give me a satisfactory approach tomorrow, I'll sure give this a try.
Beckky