Gosh generally speaking in my opinion, I dont think you can get the servo TOO Close to the control horn as long as you have the structure to support it in the wing, and you have the mechanical room in the linkage. You will just need to make sure that you set the control horn in the right relationship to the servo to get the geometry you are looking for.. I would think that dual axis rod ends would give you a little extra freedom of motion so that the pushrod doesnt bind up at the servo arm or control horn.. On my Genesis,, the servo is so close to the control horn that I had to clip the threaded titanium rod ends for the CF pushrods off because they were too long end to end.

Assuming that the servo arm is pointing to the fuselage, I like to setup my geometry so that at full throw on my highest rate setting, the pushrod is parallel to the long side of the servo and paralled to the control horn, this equals max leverage at full throw.
When it comes back to neutral, the pushrod is angled slightly from the servo arm to the control horn and is no longer parallel to the servo. This should give you increased mechanical advantage as throw is increased and less at center, which is what you want... If you start out at neutral with the pushrod parallel to the servo and at 90degrees to the servo arm,, it looks pretty, but as as throw is increased the pushrod angles in or out and you are losing leverage,,, at least thats the way I understand it.. If Im wrong thats fine but thats the way it was taught to me and looking at it it really seems to make mechanical sense.

You are welcome for the unsolicited free geometry lesson!! lol