Actually you have that backwards at the control surface horn just like in RC the innermost hole will give you more throw, the outermost will give you reduced throw. I would suggest using the outermost hole on the elevator horn.
As for the Cox handles, Yes they all are short and there was a variety of them but most if I remember correctly had three available holes and with that stabilator I think since we are using centuries to describe when we last flew controlline
I believe if it were me I think I would go to the middle hole.
At he handle the further the lines are apart the more throw at the elevator. It is as if your hand is the servo and the handle is the servo arm.
Good luck on your first flights and enjoy, Don,t forget to come on back to share you success with us.
John