A 6.1" 19.5:9 device has an dimensions of 2.56" x 5.54" and an area of 14.158 in[SUP]2[/SUP].
A device with that area, rounded to 3 decimal places, and a 16:9 aspect ratio would be 2.82" x 5.02" with a diagonal measurement of 5.7562", or basically 5.76".
If you want to be really bored I can explain how I got there.