Double foil offers better heat management and consitancy. Plus it stays tighter and doesn't sag so easily into the shisha.
Foil ring is for a shallow bowl, if it is impossible to keep from buring the shisha.
I think anything more the 2 layers would be wasting foil and coals. Take more heat because of the added thickness.
Yea triple foil is kind of a waste. I use 2/3 of a sheet of foil per bowl...which I fold over on itself once. The 1/3 left I stick in a can to use as a charcoal holder.
As for the foil ring, I could never get that right.