Basically all pickups with equal pole pieces as the number of strings have a design flaw. If you notice Fender style pickups using 6 Alnico rod magnet pole pieces, the A-5th, D-4th, G-3rd, B-2nd poles each have a magnet on both sides of it. For example the A-5th pole has the E-6th pole and the D-4th magnetic pole pushing against it. On both bottom E-6th and high E-1st there is only one pole along side it producing a different magnetic field for the string vibration in those two positions. A magnet is in a pickup basically to magnetize the string and when the string vibrates, it moves the magnetic field back and forth through the coil and produces an alternating current that travels through the controls to the amplifier.

For proper magnetic and electrical phasing all pole pieces should be of the same polarity such as: (S-S-S-S-S-S) or (N-N-N-N-N-N) and never (S-S-S-N-N-N) or (S-N-S-N-S-N) in the same single coil pickup. You could experiment with different pole polarities (North or South) to create different tonalities in the pickup. By changing the magnetic polarity of one pickup can effect the sound when combined with others.

Never remove or reverse rod magnets in single coil pickups with fibre bobbins as the coil is probably wound directly around the magnets and removal of the rod magnets can break the inner windings of the coil.