When the argument --start-fullscreen is added to initialize google-chrome in normal mode it seems the screen size is:
1366 x 724px
Snapshot:
Whilst google-chrome-headless when initiated additionally with either of the arguments:
--start-maximized--kiosk--start-fullscreen
The resultant screen size is always:
800 x 600px
Snapshot:
Conclusion
So it can be concluded that in --headless mode Chrome browser always opens in 800 x 600px size ignoring the customized --window-size arguments.
