I notice if I preview the text, as shown in the screenshot below, it previews it in a 640×480 pixels window. I also can't drag to resize this window.

I assume most players are going to use an at least 16:10 aspect ratio but probably even wider like 16:9 or 21:9.
So is there a way to change the preview size, to for example 800×500 pixels?

I have already tried changing the resolution in the System Manager, but while that changes the resolution when playing the game it does not change the resolution of the window.