It's a balance, with a wide range of "best" numbers.  Basically, how far the pushrod hole is from the center affects the ratio of leadout motion to pushrod motion.

Too close, and the pushrod doesn't move much.  The forces on the pushrod are higher, and you need a shorter distance from the pivot on the flap (or elevator) horn to the flap hinge line.  This means that you're putting more stress on your flap horn pivot points, and that any slop in the linkage is magnified compared to a longer pushrod to pivot distance on the bellcrank.

Too far, and you need to find room for all of the workings.  Slop has less effect (which is nice), but now the fact that the bellcrank is rotating out of the plane of motion of the flap horn makes more of a difference, so it may be difficult to get the flap deflection vs. bellcrank deflection symmetrical (you'll see some folks obsessing over this -- it's the reason for various oddball doglegs in flap horns, tilted bellcranks, bellcranks with pivots offset fore or aft, etc.)

Like a lot of things in stunt, this seems to be mostly settled: the current ratio of somewhere around 4:1 between the leadout spacing and the pivot to pushrod hole seems pretty good.  Folks will deviate from that, or make tweaks (like tilting the bellcrank or offsetting holes), but by and large we look at the top dawgs, see that they aren't markedly different from "traditional", and go with tradition.

The only real exception that I can think of to this is for Old Time stunt -- if you're building a Ringmaster, or some other plane with a ginormous elevator, then to keep it legal and have the thing work decently you really want to reduce the movement of the elevator.  This means either moving the pushrod in (on a Ringmaster you want it at about 1/2" away from the pivot), or having a super-long elevator horn (my Ringmaster has a horn that leaves a furrow in the ground when I land).  But that's not an aerodynamically ideal situation -- it's doing the best with what you have, to stay within the rules.

What do the Old Time Stunt rules have to do with anything about the bellcrank/control system in a Ringmaster?

Keith

If you move the hinge line back to make the elevator a reasonable size you render the airplane ineligible for competition.  That's where the rules come in.  Since you can't modify the aerodynamics, per the rules, you have to work around the fact that there's a barn door back there.  Where a Flight Streak or a Skyray 35 elevator would move +/- 30 degrees, a Ringmaster elevator needs to move more like +/- 15.  The next-easiest solution is to slow down the controls.

If you build the plane with "ordinary" controls you can slow things down with extremely narrow spacing at the handle -- but then you hit the Netzband wall, because the springiness of the lines is amplified by the overall control system (handle-to-tail) geometry.  If you want positive control (as positive as you can get, at least), then you want to arrange to get the +/- 15 degrees motion at the elevator with full deflection of the bellcrank -- that necessitates the on-plane control geometry I'm prescribing.

I need to re-read it a few time to see if I get what your are saying

Thank 'cuz I left out the summary: if you have to ask, just do what everyone else does.