So on your western saddle there are two front rigging holes and you use the second one from the front? And a buck strap? I've never tried a Western saddle that way. Hmm...Do you think that releases pressure off the front of the tree and away from a longer shoulder?
In a center fire rigged endurance type saddle, the 2 billets (billet and buck strap so to speak) come together like a Y meeting at the girth ring. They meet right about in the middle of the horses side and the girth goes around the belly several inches further back than a full girth position (a straignt line down from where the one on the pix is). A center fire rigged saddle eliminates the need for a buck strap, since the back billet holds the back of the saddle down.
Actually most of the endurance and Australian saddles are set a bit further back towards the midline and girth about 2" further back than a normal Western full girth, the girth doesn't sit way up under the elbows. It frees up the shoulder some. What kind of pad are you sitting it on? One made for the saddle? There are some new girths made for the torsion treeless saddles that are curved, so they fit in the groove where the regular girthline is, but the buckle ends point either back or forward it's reversable depending on how your horse is built.