Whether or not the lines are crossed is of no particular importance. As long as you have some positive Ackerman in the installation and that there is no binding at the extreme positions, either work equally well. Lines do not have to be parallel and the horns and servo arms do not have to be of equal lengths from the pivot point to the attachment point, just make sure that when the servo throw is at it maximum, there is no binding anywhere in the system. I've been using pull-pull on all my large models (and many smaller ones) on both elevator and rudder with no problems. I often vary horn length or servo arm length to control throw angles and doubt if they are ever of equal lengths.