Here's another D. O. thread with some extra info:
http://weberkettleclub.com/forums/grilling-bbqing/dutch-ovens/I put a link to the Boy Scouts page that has # of coals per temp there...........
On lid coals is more for actual cooking / baking, so if you start with par-boiled, but not almost finished beans, that's a way to go.....
for canned beans that are pretty much cooked, or par-boiled & simmered for awhile before kettled up, what I do is more like doctoring them up with spices, honey, sauce, etc. then smoking them to add another flavor layer.....so it really is sort of a "pick your starting point" kind of thing......am I describing this well enough?
You can place coals all around or bank & go opposite & just rotate the pot a few times 'cause it will heat more on the side closest by a bit............