RE: pull/pull wire crossing
With crossed wires there is NO geometry that will exactly maintain the same line tension.
With straight wires, you can set the length of the servo arm to the same length as the control horn and achieve a perfect parallelogram. the lines stay the same tightness throughout the range of motion.
If you don't believe me about the crossed lines, draw it up in CAD and measure the lengths of the wires. Draw up something that looks like this attached picture.
Draw something like the first picture with both the servo arm and rudder horn the same length. measure the distance of the "wire" S1-R1 and S2-R2.
Then draw the next picture with the servo arm at 45 degrees and the rudder at 45 degrees. Measure the two "wires". They will not be the same as in the non-rotated picture and the sum of the two lengths will not match the sum of the original (unrotated) wires. No matter what angle you draw the rudder, you will not be able to get both wires to match the original drawing.