i think there aren't factory specs for pickups height as it's a rather personal taste thing, i guess.
you have a volume gap between the pickups? i assume the neck p-up sounds louder than bridge p-up, right? if so, lower the neck pickup by loosening its height screws right on its mounting ring. usually, on a guitar like that, the pickup should rest flush to its mounting ring, i guess (that's how i set pickups height usually).
rule of thumb:
too high pickup > more magnetic pull, more attack, more volume, dirty sound, shorter sustain.
too low pickup > less magnetic pull, more sustain, clean and natural sound, more dinamics, less volume etc.
i usually never set them higher than half the gap between their mounting rings and the strings.