a fixed pulley on one end with a single rope, is a 1:1 you gain no mechanical advantage only the ability to change the direction of the force you are applying.
with the line fixed at one end, the load on a pulley, and the line going through another block,
http://images.yourdictionary.com/block-and-tackle IE simple block and tackle you end up with a 2:1 mechanical advantage, ie you have sacrificed distance for the mechanical advantage. to move 200 lbs one foot, you must move 2 feet of rope. this is how you suddenly became "stronger"
this is essentially a double purchase system on a sail boat... the servo arm is your load, sheet starts at the boom through the fairlead, through the winch arm, and then deadmans in the hull in the direction of the fairlead
http://www.theamya.org/hints/images/mcivicfig03.jpg this setup doubles your sheet travel, but increased your load. essentially a block and tackle only working in reverse...
each time the line passes through a block it shares the load. int he RC world for those who want to stay with the arm setup for simplicity, we sacrifice load for distance. Very easy to get a more powerful servo and wire it to rotate 180 and throw in a double purchase. to get the needed sheet distance.
I'm not doubting that you get your distance, i'm doubting your math on the quadrupling of the load your servo can now take..
I drew up a picture of your setup...does it look like this...