I know this is a old topic but even after reading dozens of comments i couldn't solve the problem. With hdmi plugged to raspberry everything is fine. When I don't plug HDMI my resolutioin is too big(in scale automatically vnc option) and small in scale to 100%. I've tried to modify parameters in config.txt but nothing. Maybe there is a conflict between config.txt and something else? I don't know I am a bit ignorant with this.
I try to post my config.txt. my uncommented rows:
*--uncomment to force a console size. By default it will be display's size minus
--uncomment if hdmi display is not detected and composite is being output
--uncomment to force a specific HDMI mode (this will force VGA)
#hdmi_foce_mode = 1
I also tried to uncomment hdmi parameters. but nothing. What could I do?
Thank you everyone. It's been all day i'm trying to solve this problem