So, anyhow...
My theory (yes, Howard, it was a theory before I started building low AR tails...not after) was fairly simple.
Tails stabilize and or "direct" changes about the pitch axis of the airplane by producing varying amounts of lift which control the rate at which pitch change takes place.
As has been discussed, lift for a given area is influenced by more that just the area and the amount of camber modification which results from deflecting the movable surface.
Perhaps the most prominent of those "other things" is the aspect ratio of the surface. High and low aspect ratio surfaces of a given area are capable of producing more or less the same amount of lift--and, as a result, redirect the pitch proportionate to the lift they develop. Lots of lift, rapid pitch change; lesser lift, slower rate of change.
The thing that is differs between high and low ARs is the angle of attack required to produce the lift necessary for a "desired" rate of change. By and large, high ARs produce that amount of lift at lower angles of attack (less deflection) and low ARs at higher (greater elevator deflection). The primary source of the "different" angles of attack is the deflection of the elevator. The low AR will require more deflection than the high AR.
As has been earlier discussed, the high AR will result in (all other things being equal) the desired rate of change at a lower angle of attack (less deflection, less control input, more sensitive response per unit of input). It will be more sensitive in response rate in ideal conditions and flying in winds will require more "adaptation" to the changing airspeed in maneuvers and the inputs necessary to adapt will be more sensitive as well. Put a 10 to 1 AR tail of equal area on your Impact or TP and the response will be dramatically different from the ~4.5 or so to one on the stock bird. Yeah, you could probably trim the airplane and adjust handle spacing to make it usable but it would always be sitting there waiting to catch you unaware.
Now to the meat and potatoes of my "theory".
There is a big difference between producing the required amount of lift for a given rate of change from a low versus high AR. That difference is the amount of drag resulting from the production of the same amount of lift. I believe we can agree that lifting surfaces with a 30 to one AR (sailplanes) produce the lift required for a given task while developing little additional drag. They are very efficient and can adapt to significant different missions with very modest changes in the cost (drag) of doing so (and, by the way, ask little in the way of thrust to keep them functioning efficiently). Put that same area into an airplane designe for high speed flight and, when slower flight is demanded, for landing, etc. the drag goes up dramatically and lots of power and high angles of attack are necessary to keep in functioning as required.
When these effects of aspect ratio are applied to tails the drag produced by low versus high ARs to produce the lift required for a rate of pitch change varies significantly. Little drag increase for a very high AR tail and lots of drag for a real low AR. In the days of Fox .35s increasing drag may have been an issue. In today's stunt world, much less so.
There is an additional effect from increasing the drag per unit of lift from the tail by lowering the AR. Doing so moves the Neutral Point (the point at which all of the aerodynamic loads acting on the vehicle are "centered") of the vehicle aft (like adding more feathers to an arrow) which simultaneously increases the static margin (the distance between the CG and the NP making the vehicle "more" stable in pitch. The greater the pitch rate commanded the greater the lift, the greater the drag from the tail and the greater the aftward movement of the NP. The result, in my theory, is an airplane that is more stable in pitch response despite an aft CG that allows the aggressive maneuvering required to wing toy airplane "trick" events. It is much easier to fly into and out of a corner because the airplane's response will be less "twitchy" for a given rate of change than one with a very high AR tail.
In "Ted's theory" there is a certain element of the holy grail in finding an optimum AR to the tail and my feeling is that something lower than the AR of the wing is probably "better". As in all things stunt, I think extremes must be avoided because we must combine aggressive response with controlled precision. It's easy to make a stunt plane turn quicker than you can fly it competitively and one of the ways of doing so is to use "very high" AR tails which will produce explosive amounts of lift with very modest input. Great if you've got Superman's reflexes but not a viable source of trophies for the mortals among us.
All of the talk about hinge loads are valid, by the way, and militate against excessive use of super low ARs. Enough line to tension to deflect very low AR, large area elevators against the airloads is a real issue and can't be ignored. Other things that will effect the "optimum" will be flap size and deflection and the negative pitching moments which result that must be overcome by the tail.
At any rate. That's more or less the thought process that led me to use lower AR tails. I've been very comfortable over the years with the TP series which, I feel, provide very predictable and controllable responses under a wide range of flying conditions. I think the modestly low AR tail plays some role in that.
Ted