Greetings,
Proximal means closest to the player, distal (distance) refers to the opposite. The proximal side of the jack doesn't touch anything but the stop felt, and the distal edge of the jack aligns with the distal edge of the knuckle's core, etc.

By setting the jack closer to the performer, (proximally), the process of escapement is shortened, ( assuming a beginning point as that point at which the tender touches the pad and/or drop screw touches the drop pad), and greater danger of it skipping out under a ff blow. It is a trade-off, (like the mix in a carburetor ie, maximum response is right next to engine failure), The farther proximal they are moved, the more consistent the tech has to be, or the law of averages will visit, usually during a climatic moment in performance, and a great, crashing, note will be missing. People remember that for a lifetime. DAMHIK
Regards,

and the leverage at the beginning of the stroke is higher. Cheating jacks can be tested once, twice, etc..

<it is amazing how much we can interfere with hammer acceleration, just with different type of jack location.

DAMHIK? Wow, sounds scary! :-) Hope you weren't working for Horowitz at the time! :-) :-)

Here you can hear how is the sound with light hammers :

http://www.youtube.com/watch?v=6dXUgPVjnD0&feature=share&list=PL550F1747A716EEA7