Big-big plus 1" is preferable to small-small unless the user has done their homework wrt RD capacity. Lately, I've figured that since I don't save leftover chain to patch together later, I might as well use as much of it as I can. So, I add any leftover RD capacity to big-big+1", and round up. In the end, it may hang a little slack in the small-small, but I try not to use that combo anyway.