the prusic knot doesn't need to be against the knot at the end of the rope. it's designed to tighten on the green rope with pressure. i keep mine close to the loop around the tree so if i would fall, it will grab sooner, rather than fall 5 ft beforethe knot at the end of the rope is reached.

i thought the green rope was a good idea. it's easy to move up or down the tree as you climb/descend. that's when you are most likely to have a fall and should definitely be used then.
it's definitely a puzzle the first time, but after that, it's pretty simple.