Okay.... I must admit that I'm now out of ideas and out of my depth. Best bet now is wait and see if Any Hughes notices the thread and chimes in.
I just saw that in the manual elbows are advised to have an RP, although the elbows we've been using don't have one and we have based our elbows on existing ones in the library that came with SW.
The best bet for making any piping part is to use the routing wizard but then again... the routing wizard doesn't help at all for elbows.
PS: any particular reason you want to start from an elbow ?