When the rudder is at 0 degrees, the mechanical advantage between the reduction gear and the tiller is about 1.5. As the tiller swings, the mechanical advantage progressively increases to nearly 3.0 (almost double) as the rudder approaches "hard over". This can be very useful if you are battling weather helm when underway.
The Jefa website has a more in depth discussion here.
What's more, if one wants the steering "constant", simply aligning the reduction gear, such that it's tiller arm is on center with the rudder post, will reduce the mechanical advantage to constant.
Or, aligning the gear somewhere in between will give you less of an advantage but more than constant at extreme rudder angles.