I'm not sure what you mean by "node" but I will breakdown pickup placement for you in a little greater detail. Starting at the most basic... Pickups are placed in general ares... not neccessarily in super-specific areas. Neck pickups are placed farther away from the bridge for bass tones (as said before) because the strings eliptical pattern of vibration is larger, making the vibrational frequency larger and more bassy... the closer you get to the bridge the tighter the eliptical vibration pattern becomes and the tighter the frequency ranges become... making treble tones. The middle pickup is located in the dead center of the two... The only pickup that has a generally crucial placement is the bridge pickup. If you get the bridge pickup too close to the bridge the tone becomes more of a twang (telecaster style) and if it's way too close you won't get much sustain and you will get a deadened string. sound. The other pickups are generally placed in relationship to the bridge pickup. Slanting pickups... such as the s-s-s Stratocaster bridge pickups are slanted for tonal reason. This is to compensate for the larger string guages of the bass strings... The bridge pickup is placed in the "sweet spot"... a place where the tone is clean but just on the edge of being too twangy... The larger the string gauges the farther the "sweet spot" is away from the bridge. This compensation allows maximum bass tones and treble tones accross the entire pickup. the middle and neck pickups don't NEED to be slanted because they are far enough away from the bridge to get a clean tone without twang or deadening the strings. As for humbuckers... humbuckers generally follow the same rules, however, the bridge pickup is placed parallel to the bridge... therefore it must be placed slightly farther away from the bridge to allow for a natural tone. Other than that manufacturers don't use much science in the placement of pickups... I hope this information can be of some help to you!