When I heard before that the magnetic pull of pickups that are set too high can damp strings' vibrations, I thought it was some kind of BS. Now I've learned that this effect is very real.
I got a used Yamaha RBX-170, the action on which was too low for me and the pickups too high. As it was, unplugged, it sounded a bit "plastic-ish", and when plugged in, the tone was somewhat lacking in the deeper low mid region (if I identify it correctly - I'm not that good at frequency detection). That was largely OK for the price. But then I increased the action and lowered the pickups, and immediately the bass started sounding better even unplugged! The tone became fuller, deeper and woodier, and the sustain increased. Of course, all of this improved the plugged-in tone accordingly.
So, live and learn
