Feels like a hangover...nothing seems to be unfolding correctly. For starters, Tricia is on Ann's Asus. It took awhile but even a blind squirrel finds an acorn, right...I uncovered the Take Screenshot. Then it took another 5 innings to locate the Picture folder but I can't even right click to view or enlarge the saved pic. nothing is easy with this O/S.
I'v got you all setup (Linux.org) on my own computer (Dell desktop) but it's Win10 and no Linux. Our desktops are in Honduras that have the multiple Mint 18.1 and 18.3 on each of them where I could more easily do what you've asked me to do, Wiz. Sorry but I simply don;t know how to get around in this new O/S. Somehow I either have to get that screenshot on Tricia over here to my Win10 so I can attach it to this post...and I've run up against a brick wall. My Bad!
Dick, take a look at the screenshot attached and see if it is the sort of size and clarity you are seeking at the login screen. This is from my Linux Mint 20 'Ulyana' but I have done the same thing with my/your 19.3 Tricia Cinnamon.
It's not a scalable solution (yet) you get the default, or you can get Larger
Let me know if suits, and I can go on with more detail.