I always thought, and I can be wrong, that this horizontal buttonhole near the waist, is a leftover from previous times. In the old days, shirts would have a buttonhole on the left hand side with a loop of folded fabric attached to the right hand side. You pulled the loop through the buttonhole and buttoned the whole caboodle into the waistband of the trousers; thus preventing the shirt from riding up. Today some evening shirts still have this arrangement. I remember, some years ago, seeing Â the shirts some London shirt maker (forgot who it was) had made for the then Prince of Wales (Edward). Some fifty years later when the wardrobe of the Duke of Windsor was auctioned in New York, they bought their own stuff back. They were beautifully made and all these shirts had the buttonhole/loop arrangement as described.