I'm constructing new pickup covers for a bass with lindy fralin Jazz style pickups. I'm quite new to this and one of my concerns was how thick the top of the cover should be for the pickup to still pickup the vibrations of the strings. FYI: I'm constructing the non-exposed pole piece type covers. If anyone has an idea of how thin the top of the cover should be or what range there is to where the pole pieces can no longer pickup the sound, please let me know. Thank you!