My experience with VNC is - which I admit is not that extensive - that you cannot dynamically change screen size.
You need to set the screen size in the configuration on the remote system.
I have played with VNC on raspberrypi and even with the licensed RealVNC you need to set the screen size for the screen served from the Pi.
So in my opinion the solution is to set the desired size as described in the TigerVNC article.
A proof of concept can be found in my previous writeup