RE: Correct Control Line for 1/2A ??
There is no compelling reason to use the supposedly "1/2A" bellcranks of about 2" between leadouts. That smaller 'radius' is what makes it important to use smaller line spacing at the handle to kill the excess twitchiness 1/2A models are usually thought to suffer.
Smaller line separation at the handle means also that line lengths become more critical. If they aren't perfect, 'neutral' (level flight control input, where the flier can relax a second or so to get back on top) is hard to find, and a mismatch makes things not as natural...
My recommendation is that, if possible, use a 3" bellcrank and matching control horn(s) for the same feel a larger CL model enjoys. Our hand, in the handle, tends to reach the same 'stroke' regardless of the size of the model. If the bellcrank and horn(s) match our comfortable "feel" even the quickest of 1/2A models feels more 'solid' and controllable.
For a built-up, or plan-based 1/2A, it may be simple enough to change to a 3" bellcrank... The weight penalty is modest, an aluminum 3" bellcrank weighs not much more than twice the typical nearly weightless nylon 2" 1/2A piece, and is worth that for the more comfortable 'handling' it provides.
BTW, IMHO 0.012 braided lines don't degrade the flying of a sport 1/2A at about 35' length. For more capable flying, with more powerful engines like the AP Wasp 0.061 or Brodak .049s, longer lines are necessary because they reduce lap times to what an ordinary human can survive. THEN Spiderwire or other exotic solutions become very useful. But, if you can still find them, 0.008" braided steel cables are not only great to use, but are acceptable for AMA Rules events.