Ok - a bit of research into Windows 10 and scaling suggests this is a work in progress by Microsoft, and the user's experience and what they can do about it will vary depending on what version of Windows 10 they are running.
Here are a few articles I have found on this:
If you want to support high DPI properly, then you probably need to implement High DPI functionality as described here:Overview of the High DPI technology
If you are on 1703 or later (or possibly 1709 or later) then there is a compatibility setting:
I am not at my laptop right now, but I will test this later to see if it can help.