I think you might be having a problem in 2 different places here.
1, you've got new saddle pads under it and the pads do not appear to be contoured so they are basically in a straight line from his withers to his hips, not dipping down like his spine does. That can cause the back of even a well fitting saddle to pop up.
2, this is a common problem in saddles with the rigging in the full position (Western Saddle Rigging
) because every bit of the pressure from the front cinch is being placed directly on the very front edge of the bars. A rigging in the full position works great for roping saddles where you've got the back of the saddle strapped down tight with a back cinch, but on regular pleasure saddles, many of which don't have a back cinch at all, then all it does is force all the pressure onto the front edge of the bars and throw the balance of the saddle off.
I'd say that, no, this saddle doesn't fit well enough for consideration long term. I'd start looking for a different one, preferably with a front rigging in the 7/8th or 3/4 position as those will balance the pressure of the cinch better along the entire length of the tree instead of just at the front.