Rich would easy be the best person to give tips on kitelooping, but I've been trying the F16 style loops for ages (getting blasted most of the time mind you). I think with shorter lines it's definitely easier to get above your kite and get that powered yank, but for some reason you don't seem to get as worked when you come hooking in to land. Maybe because the kite doesn't have as far to go to get out of the power zone? I haven't landed many trying with the longer lines, even if you go big you drop like a sack of ****, and dropping without any lift from the kite makes you feel like your knees are gonna explode. I tend to use the kite to get the lift, pop off the water, then loop the kite. I think it might be better just to crank the bar the whole way through the turn. It might be enough to get the kite a bit higher so it can take some of the impact out of the landings.
Probably not a very useful answer, but at least I can tell you what doesn't really work

PS. That being said, I still think they are ****in fun and I seem to be going back for more, just watch the knees.