Help.. Girths (again, sorry )

The Stubben may bunch in what I call a "pouchy" girth groove ie a deep, short and very defined groove. It's wide for starters and obviously has no structure, so it's the one case where it's likely to be a problem.
 
F has a forward but wide girth groove. The Stubben cord is fine mostly. The straight Dever removable neoprene has slight folding behind each elbow.
The Stubben doesn't stop the saddle slipping forwards slightly on very steep down hills. The Dever didn't slip.
Saddler and I have tried many girth / saddle combinations.
 
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