I use a square wherein the landscape and portrait portions intersect in the center like a cross. The corners are just black as they don't get used. In theory this should work, just like it does on most any device, but for some reason iOS 7 through current screw up landscape unless it is one of their pre-installed backgrounds. Never figured out why, nor how to correct the issue. Perhaps Apple applies special code to their own backgrounds but not to customized ones. Oh well, I guess we are stuck with it.