I like the midpoint method because it gives you a way to cover any little glitches that occur - if something isn't exactly square it will not show. The support cannot be ignored either, but no matter where you put the joint, you should have some sort of longitudinal support as well. I see absolutely NO difference in coming up with the correct OAL being caused by the splice location. Just me. Haven't actually done it yet but I have a couple of projects in mind.