David, that is a good illustration. I tend to agree with your 65-foot length. I always found 50 to be too short and 100 was too long, so 65-70 was best. For a heavy food weight, more length is useful. It depends on what kind of trees you have.
Instead of bear bells, we used to tie our metal cookware onto the tree. The bear sees about four or five cook pots, each with a rock inside, and wonders whether he really needs to climb that tree. The rock rattles when anything moves it.
For one tree, we used to wrap a space blanket around the trunk. The bear would look at it and wonder what that was instead of climbing it.
The half-grown Yosemite black bears were the worst. They had no fear of falling off tree branches. Sometimes they will see the branch with the food bags, and they climb above it on the trunk. Then they jump off, hoping to catch the food bags on the way down. Those were called Kamikaze Bears.
–B.G.–