Sliver,
First, I apologize. I thought I was talking to a fellow Foxist named "Silvers."
I suppose, ideally, you might want 100% contact of barrels and face. And you might want most of your contact at 3 o'clock. But by the time I undertake to put a Fox back on face, the barrel flats will have contacted the watertable and there's enough slop that the bolt can't hold them in contact during firing. So the first my first move is to set them up and back, contacting at top, not at bottom. As I fit, I strive for 90+% contact across pin/hook, but with interference at the top of the breech. I'm not good enough to fit with 100% contact, and don't know enough to say it's desireable.
The relief at bottom provides for compensating movement as the gun wears, allowing the rotary bolt to do its job of snugging the barrels deeper into the face.
I have a couple old graded Foxes with virtually no wear and smoking and shooting them shows me where, and how much, contact I should strive for. Maybe a pro will chime in and save me.....maybe not.
best, Mike
