IMHO, the easiest and best way to reduce 1/2A models twitchiness is to put a "full-size" bellcrank and matching horns in it from the get-go.
Control surface deflections will feel more natural; they'll be much more like what we learned on, presuming you learned on more usual size models.
Closing down the handle line spacing can get to the point it is hard to manage, and comfortable width spacing may make just too much input unless we practically lock our hand rigid. Simpler: 3" bell crank and matching horns... Shouldn't take too much fiddling inside the structure..
Try it - you'll like it.. (whose slogan did that used to be..?).