Yah, drop the height. Too many (sorry) ****ers put the poles within 2mm (or less!) of the strings, figuring they'll get more volume or power or sustain or wtfever the current buzz-word is. Well, they do get it, at the cost of tonal coloration. I've had a few customers that I could've gotten to pay me for replacing their pickups, when all I did was give the screws a few turns -- but, I at least attempt to be honest.
If the pickups were installed aftermarket, then it's possible there's a tone-knob short & a capacitor is stealing high tones.
If that doesn't help, then consider "cooler" pickups (lower ohmage) or speak to a winder about changing your magnets.