I have the opposite problem. I rent a medium size P.O. Box and have a lazy "box clerk" at the post office who will not put small parcels in it. Instead, he or she just puts tags in all the boxes so we have to stand in line at the counter to retrieve packages that would clearly fit. If I didn't already have so much invested in my actual P.O. Box number as my business address, I would switch to the smallest (cheapest) box available.