Years ago I cut mat windows and mounted prints with the image slightly above center. No longer. Now it is usually 10x14 prints centered in a 1" larger window which is also centered in 16x20 mats. Precut mats ordered in quantity are as inexpensive as 16x20 mount board. They can be used for portrait or landscape formats. After decades of exposing and projecting 35mm Kodachrome, the idea of making the image capture fit the format is second nature. My customers in rural Missouri appreciate the price savings. Of course, in a sophisticated upscale market, other rules prevail.