The recent SBL Geddy Lee vid that was posted elsewhere talked a bit about the "clank" you get from moving your plucking position closer to the neck. If you watch vids of early Geezer, Geddy & the Ox, they all play closer to the neck. Always thought it gave a more "plummy" sound, almost double bass-ish, but if you play a bit harder, it does have that bit more of an attack.
Another thing I've noticed is that you can get a bit more of an attack by using the side of your fingers rather than the tips. If you angle your hand a touch toward the neck from where you anchor your thumb, you can change which part of the finger plucks the string. Works for me.