Woodoworkery:
I had the same problem, but fixed it ,and can't remember what I did sorry.
I remember when you did that, I'm guessing you tried different res. numbers, and after a search on the web it's a lot of people using the wrong aspect. I think you have to enter a compatible res. e.g. 16:9
Sometimes it's a width setting, stretch, etc. maybe, but i don't know because I use a small WGT window as on my laptop the meter is much more smooth the smaller the game window. It takes less computer power to render a small screen I guess on my Dell (this varies with other people's computers, I know) so I've been playing WGT in a non-full screen mode for a while.
I would enter in several different res. and see if the bottom is still cut off.
a quick search shows a 'list of 16:9', and knowing what your WGT window is at in full screen might be key, too.
https://pacoup.com/2011/06/12/list-of-true-169-resolutions/