We've all knocked this one around quite a bit...
If you take a 5" bellcrank, and make the pushrod radius proportional to a 3" bellcrank, and make the flap and elevator horns proportionally larger, --
YOU HAVE NOT CHANGED ANYTHING! It feels like the original model using a 3" bellcrank and the horns illustrated (or provided) in the kit.
The only change is that you have 'slowed down' the response, unless you change handle line spacing by the same proportion as the on-board pieces.
It isn't that hard to build your own bellcranks and horns - I've done mine for years, except when - rarely - commercially available pieces were close enough (radius within 1/32", say).
The advantages to larger leadout and pushrod hole radii: The pushrods are under less load. If it takes 10 inch pounds of torque to turn the flap to 45°, a 1" horn radius only sees 10 lbs load. A half-inch horn requires 20 lbs. THAT force must pass through the pushrods. 10 lbs? Sure. 20 lbs, well, er, uh, maybe...?
And, if you want the same 'response rate': adjust the spacing between lines at the handle.
One of the things I enjoy in this hobby is trying to nail such relationships before I cut wood, ply, foam, wind, or whatever. Seems to have worked, leaving only me to blame for how the models fly when judged...