You also have to remember that a shorter pin to pap will make you keep your angle through the heads straighter, due to how the ball reads friction. Here's a good picture for you to imagine when thinking about it.
Take an egg, and try rolling it end over end. The egg will always find it's "PSA" (being on it's side) in a shorter time being rolled with the smaller end of the egg (top of the core) closer to the PSA than further away. The further away you put the pin (top of the egg) from the PSA and try to roll it end over end, the more it lopes, but when it starts to move towards the PSA, it will be a less smooth motion.
That, in essence, is how a weight block works. Every time I've wanted to open up a lane, I have gone with a longer pin to pap, and every time I've wanted to tighten up my angles, I've gone to a shorter pin to pap.
On Edit: This is only for symmetricals.