For non-symetrical elbows you are best to not have it auto
insert, instead have your 3D sketch do a square intersection (no
radius) and then insert your 'special' elbow as you would a Tee or
reducer. The fitting will then cut the pipe to suit (see the
attached extract from my piping library catalogue for a different
desription).
*The first shows how the asymetrical elbows were autoinserted into an Route assembly.
*The 2º and 3º, show the elbow which made this possible. I have to deal with 2 lenghts, X1 and X2. If the ratio X1/X2 >= (1.5........2) in gets troubles.