About that, when you say "0", that corresponds with maximum resistance of the pot- thus the bass end of the sweep, correct?
No, just the opposite. When the tone pot is shorted out, zero resistance, fully counterclockwise, that makes the pickup thru the tone cap directly connected to ground since the pot resistance became zero. That is the darkest setting with the full dump of treble.
When you turn the knob clockwise, the more resistance you have, and the less the treble is cut. At full resistance, the full value of the pot, that is the brightest, most trebly setting because the resistor is "resisting" the path to ground thru the cap.
When I say zero, I mean fully counterclockwise, or the darkest dullest, least-trebly setting. Essentially the pot doesn't exist in that particular condition. It's just a pickup seeing a cap to ground, fully shunting or dumping all the high frequencies that will "fit" thru the cap.
The "horn" factor we're talking about here is a more complex thing that happens when the pickup sees the cap fully grounded, zero resistance from the tone pot. The pickup, being an inductor, will actually shift its resonant frequency downward and also slightly boost at that frequency. This gives the horn effect. All magnetic pickups do it when the tone is "off", but the cap value helps determine at what frequency this happens. Jerry's .02uF seems to create this shifted peak at a frequency that is horn-like. Magnetics, inductance, resistance, reactance, capacitance, etc. is actually a very, very complex science full of complex math. Fortunately we don't have to mess with it all that much. Pickup designers and engineers have worked out many of those factors so we get to simply play around with simple values to tweak to our liking.