I run 1 account/proxy. For home IP, i used to run about 10. But some accs went dead although there's too many variables in play and can't blame it on the IP vs accs ratio.
If your accs are aged, it can survive in more accs per proxy, but if its new, then the new accs will die very fast.
Think of when you're in a free wifi zone, your own acc is working fine, but if you did anything with a new acc that acc will be banned while your own acc is fine, because it's very likely an aged acc.
To that extend, i was even thinking of setting up a long range wifi to steal some local coffee shops wifi and run off it.