What is your point?
Are you tried dpi=560? You've tried it but you saw that 560 is not the best value, which is why you use the automatic settings?
You are tried dpi=560 and want to tell that this setting is OK and that my sugestion is not good?

...through sys.txt we want to say to the program, from which folder should use graphic elements. And dpi=640 is an analogy for xxxxdpi folder, in which in my opinion is the graphics, which will best look in the application at that resolution.