Good summing up of residencies. A couple more things: all the residency flings I witnessed happened with one of the participants having only a few days left. No one wants to hook up, have it go bad, and realize you have four more weeks in close proximity to a person who is essentially a stranger with a real reason to dislike you.
And I’ve always separated out residencies by “totally free” or “not totally free,” and I’ve never applied to a residency that charges. That may be limiting but it’s also, you know, free.