"maximum leverage from the servo"..............................
An analogy:
You're going to clean out the gutters on a house. You have an extension ladder. You use it first to clean out the gutters that are over the porch. The ladder is easy to move for that 1 story reach.

Now you extend the ladder so that you can reach the 2nd story gutters. The ladder is still the same weight, but it's much harder to move around.

Now you have to get the gutters in the back of the house and they're 3 stories above the ground. You extend the ladder to reach and the first time you try to move it, you can't keep it from falling over. Why?

The leverage has gotten worse and worse as you extended the ladder. The weight of the ladder has moved away from you.

So now pretend that you are a servo and the weight of the ladder (which never changes) is the aero load (which doesn't change either). Move the servo load away from the servo with a longer arm, and the servo is less able to move that aero load.

If you want to give the servo some help, make the surface control horn longer and the servo arm shorter. This always gets somebody. This time it got the git.....