actually, the points on the surface and the points on the control horn do not have to be the same distance apart, and you will not get slack it they are. see, if you move the servo horn 1" at the tip, it will pull the wire 1" in that direction. therefore, the line on the other side will move 1 inch the other way. so, you could have the point on the conttrol surface a mile out where the cable attaches, but it will still only pull one inch, however many degrees that will be. you will not get slack because the other side will move 1" where it connects as well. it's a matter of leverage. a longer moment at the control surfaces and a smaller moment on the servo side will result in less throw, more torque. it's a comon mistake to think that the wires have to be paralell. in many cases, crossing the wires will eliminate slack due to imperfect geometry.