So basically its changing mid frequency shape. I wonder if it does this off the preamp or by manipulating the pickups like coil tapping.
I never heard of a factory coil tapped Ibanez bass. Someone can correct me if I am wrong. Probably just done with different capacitors and resistors soldered to the switch.
On a side note, I have some custom coil tapped pickups in a tele and it doesn't change the tone like a tone switch, it is more like it changes the gain and output by adding or subtracting winds from the pickup. I ordered from here: Cavalier Guitar & Bass Pickups
I have these two that each have two pickup configurations....
50/51 Lion (7500 turns) - Nocaster Holy Grail (9700 turns)
The Lion King (8500 turns) - The Fat Lion King (10,500 turns)