DaveyMo and all the rest in here: There's already lot of good advice!<

Since I made a stupid-simple discovery, my small models aren't twitchy.

Use a larger bellcrank and matching horns!

Our handle movements are just about the same whatever the size the model. I don't understand why kit mfrs and other small model designers went to the 2" or smaller "1/2A bellcranks." Cost reasons? Or possibly they thought they looked "more appropriate" for smaller models..

Our "natural" "comfortable" amount of arm/wrist/handle input could drive a "1/2A bellcrank" to a much bigger angle than it drives a 3" or larger bellcrank system. Make it even worse? Use "1/2A control horns" too.

Apology: numbers and simple math follow:-
The example numbers are not precise, or even used, but give the idea.

Remember the Sine function? Okay, well, see it this way...in a triangle with a right angle at one end and a 30° angle opposite the 'base,' the 'base' is half as long as the hypotenuse. If you have a 2" bellcrank, each arm is 1". If the bellcrank is turned 30° from neutral, it only took 1/2" of line movement to get it there.

If your handle has a 4" line spacing, the lines are 2" above and below neutral, agreed? Rotate the handle 30° and each line moves ; (2" x Sin 30°; 2" x times 0.5 =) 1" from neutral.

If you're using a 2" "1/2A bellcrank," that much line movement pulls the bellcrank to 90° away from neutral!

With a traditional 3" bellcrank and 4" line separation handle, the bellcrank in the model will turn more than 30° , but not 90°.

With a 4" bellcrank and handle, obviously, the bellcrank turns the same angle as the handle. We don't need to match our hand angles to the control surface angles, this is just an example.

Even if the control horns are "scaled" to match the small "1/2A bellcranks," a human sized handle will turn that system too far, too quickly = too twitchy!

It may not be easy to fit a 3"- or-so, bellcrank into or onto a 1/2A size model, but it makes a huge difference!

Otherwise, you could bring the lines out from the handle closer together... But, that makes finding a comfortable neutral much more critical, and you may feel that you need to move the handle further to make control inputs. Wrong, but a natural tendency...

If you want any model to feel right, use the same proportions at the handle, the bellcrank and the control horns as for models you are most comfortable with! And using the same size pieces is the simplest way to do that. Remember, you can make up bellcranks and horns that weigh less, but still have the "right" dimensions.

(edited - phrasing)