If you look at the two, you'll see the GP puts far less panel on the horse's back than the Courbette. That could be making a difference to his way of going, even if the latter is really too narrow. I t depends on the horse.
The other thing that springs to mind from the pics is your GP looks very like a foreign brand. Apologies if it's not, but the head nail and flap are very Indian-looking. If it is, then their arches sometimes flex under load, giving an apparent better fit, and if it were me I'd check the arch is rigid by pulling on the points.
Like tinyliny said it's awkward to judge fit against the shoulder with pad and mane (!). I'm not familiar with the tree shape and because of the head construction, which looks narrow, you can't fairly judge the point angle, which is the key.
Really nice looking saddle, though :)