There are 2 kinds of display:
Full screen... you have to put 1 on the line "#full screen" after choosing the size... The best is to use the options of launcher
For windowed, the OS Windows takes these values (width, height) but uses some dozen of pixels for displaying a border . You have to identify these values.
In windowed mode, you can adjust the window size with the cursor. Put it on the limit of window before adjusting. The new values aren't saved in the file initDiag.txt
JMM