You really only NEED to cross if you need to to get the right angle from the Rudder horn to the control horns on the rudder and you cannot get the right angle by crossing. In short, if you can get there in a straight line without having to cut a super long slot in the fuselage then there no real advantage that going to amount to a hill of beans in crossing. There may be some sort of mathematical advantage, but in reality as long as the cable does not have to bend around the exit hole or a former then there is not enough to gain to warrant crossing unless that just how you want to do it. 6 one way, half dozen the other.

If you do cross you need to use an offset servo arm. I am not a mathematical geometry person but for some reason when you cross you endup with the not pulling cable going very slack if you do not use an offset arm. The offset arm somehow allows the backside cable to stay tight when it is not the pulling cable.

Also, if you do cross try to install the hardware so that one wire is connected on top of the servo arm and the other cable is attached at the bottom of the servo arm. This will help prevent the cables from touching at the point where they intersect. Touching cables, especially if the cables are wire (I use Kevlar) they can create interference in you radio system.