War sez:
Hit however you want, but move fast, aim between the joints you want to dm, and ghost into uke a bit. If you ghost into him, you contact more joints at once and you spread them apart from each other, so the force keeping joints together damages them more and makes dms easier.
I find the best speed for a boom to be 35-55. I've done one at 60, but it was all luck. Too fast and you ghost all the way through, too slow and you don't get into uke far enough.