Orion, "As you no doubt know, the 100 grains or so of metal rod in the front does a lot more to increase the foc than a hardwood footing."
Yep, the footing is for durablity behind the head more so then FOC.
"It also seems to strengthen the area immediately behind the head, since the metal rod normally extends back into the shaft another inch or two."
I'm sure it does but it's probably a moot point since hickory doesn't tend to fail there even without the metal insert. I do it just for FOC.
"I shot them into a solid oak, broke the shaft mid shaft on a glancing shot."
Yep, those glancing shots are a bugger as 99% of bone hits would be. That's the reason for the staggered footing points. If all 4 end at the same place, that's a weak spot. We need our arrows "tillered" like bow limbs or fishing rods!
....O.L.