Crescent girth? (saddle wants to slide forward)

I have a very dramatic young mare who is a very tough saddle fit. She’s a little downhill, with a big barrel, narrow chest, and forward girth groove. She is a diva about all things and doesn’t have the best work ethic. If the saddle slides forward, even a little (which it always wants to do), she acts like her shoulders are blocked, and is pissy and/or doesn’t want to go forward, especially at the canter.

The saddle fits her well and was adjusted/re-flocked for her this summer (and we’re on the schedule for a re-check once my fitter returns from Germany). But the biggest issue seems to be the girth pulling the saddle forward.
Things I’ve tried:
no slip pads, different pads, half pads, no pads
shoulder relief girth, neoprene straight girth, equalizer girth, shaped girth, loose girth, tight girth

A crupper is a hard no with this one, even if I could find one large enough to fit. For now, I will often get off mid-ride to set the saddle back an inch, but it’s hard to do that when we’re hacking out.
A new saddle isn’t in the budget, but I’ve had two different fitters (including the one referenced above) note that she’s complicated, and agree that the saddle itself is the best we’re going to get. She’s a hunter, so not interested in trying treeless saddles or other non-traditional tack.

I’m intrigued by the Mattes crescent girth. I wonder if the shape would allow the bottom of it to fit into the mare’s girth groove while putting equal/downwards pressure on the billets, without pulling them forward. It’s a lot of money to spend and I can’t find a cheapo knock off. I’m hesitant since the TSF girth didn’t work At All. But I’m desperate for something that lets the saddle stay where it belongs.
Anyone had one/tried one? Did it work for you? why/why not do you think? Is there any such thing as a custom shaped girth? Where would one get this and how do you measure/make the template?


That is what the girth is for, so I think it is worth a shot? But I’ll also add that saddles may do this with this kind of horse if a touch too narrow. And that’s in the tree (tree points as well as base of the withers near the stirrup bars) and/or in the shoulder fit (front panel area).