Instead of drop shadows try using graduated screens, darker to lighter, from the top/bottom to give you a little more contrast to make the copy stand out more.
You're right, Dave, Wayne makes plenty of bonehead mistakes. Ask anyone. lol Unfortunately, there's nothing you and I can do to make sure it happens 100% of the time but the stickers are supposed to go on the address side of the mailing.
I'm gonna go out on a limb here and assume the Post Office's intent is to keep the content side of the mailing free and clear of stickers and anything else that might interfere with the message. Anyone in their right mind paying good money for postage would and should demand compensation from the Post Office when they intentionally and repeatedly deface mailings designed to the Post Office's own specifications.
Wouldn't you agree?
Even with the address side, while I do see one every now and again -- maybe once or twice every couple of months -- in my neck of the woods those stickers have largely been replaced with ink-jetted bar codes. Just MHO, while it's wise to keep it in mind, designing everything so the occasional bar code label never intersects any part of the content could be overkill.
A 4" X "6 postcard gives you 24 square inches per side to work with, 48 total. Since we so rarely see them out here I don't have one to measure but the labels I've seen are maybe 3/8" X 4". If I'm right, the area they cover is 1.5 square inches. For the sake of argument, let's double the height to 3/4" or 3 square inches.
For what it's worth, and, again, just MHO, and I realize we're working with fractions of a second to catch someone's attention before the piece goes in the trash, but I suspect if the 93.75% of the message not under the sticker hasn't generated enough interest to cause someone to peel away the occasional, pesky bar code label, the 6.25% under the removable label probably wouldn't have made the difference either. On the other hand, not utilizing that same area because some small percentage might get covered with an easily removable sticker is a tragic waste of valuable real estate.
Food for thought.....