Looks as though petrov27 has found what is needed.
As an aside and addendum to my last post, I also used the PE wire in the cockpit interior, the cross wires in the upper wing above the cockpit, and the tail planes with excellent results. I can only conclude there is flexing between the wings causing the bowing of the wires. If I were to try the PE wires again I wonder if running them through the lower wing, drawing them taught with weight, and gluing would work?