I swear by copper foil for shielding electric guitars, so this is more about copper foil in general. I go beyond the recommended amount of shielding and place it wherever I can, even where I've been told it doesn't matter, but every guitar I own, from stupidly expensive to $60 foreign kits, is completely silent, regardless of amp orientation or pickup type, and I even have fluorescent lighting in my studio. Just make sure ALL the tape is physically and electrically continuous and grounded to form a full Faraday cage when the covers are brought back to the control cavities. Use more, you won't regret it. Just remember that the edges of thin metal bands are very sharp, so keep a box of band-aids nearby.