What is going on inside my magnets?
Excuse me: I thought the grinding was just to resize the magnets ... if you made them smaller radially I'd expect a decrease in strength near the poles but not smaller vertically.
Grinding is the action of cutting magnets into lots of smaller bits ... and one big bit.
The simplification for illustration purposes is just slicing the magnet in half to get two equal strength magnets.
Isn't the field gradient supposed to be created by the fact you are shoving like-poles together? i.e. not by shaping the magnets? What did you expect the grinding to do to the field? (i.e. what is it you want explained?)