To answer your question my suggestion would be to conduct some experiments for yourself. You can get interesting tonal effects by doing this. I have used the outside portion of the tap to vary the tonal response. The results will vary because of coil geometry, turn pattern/ count, gauge, magnet type and strength, and proximity of the coil to the magnetic source. Best to try some simple experiments at first with some tapped coils and come up with some formulas that work for you.
Several of the older, 60s/70s, import pickups actually had the coil not touching the magnets, while others were wound directly on, or near, the magnet(s).