I'm sure there are Tri-specific web sites that will give you guidence.
I'd route the cables so you get the straightest run to the housing anchors. I'm not sure what you mean by "in front of or behind the bars". The aero bars or the drop/cowhorn bars? I think the cables run on the underside if the aerobars and pass under the drop/cowhorns. I also guess the shift levers are set so the ends face directly forward in the relaxed positions, sort of like downtube shifters. Again, look for a tri-specific web site for better info.
BTW, is your Avatar an SP-101?