The screen man says
‘-A’
Adapt the sizes of all windows to the size of the display. By default, screen may try to restore its old window sizes when attaching to resizable terminals (those with ‘WS’ in their descriptions, e.g. suncmd or some varieties of xterm).
This works when you start off a screen with the -A flag. But, how do I set it in screenrc so that all my screen sessions get it by default?
fit
Change the window size to the size of the current region. This command is needed
because screen doesn't adapt the window size automatically if the window is dis-
played more than once.
Default key binding for fit
is C-a F.