I’m using a Dell XPS13 (3200x1800 resolution) with a UD-ULTCDL and 1920x1080 Samsung LCD. I use the monitor to mirror the screen.
When I connect the monitor to the XPS13 the icons and text etc look right i.e. adjust to 100% scaling, but if I then disconnect the monitor the scaling stays at 100% so everything is TINY on the XPS13. The correct scaling for the XPS13 is 250%. I have to reboot to make it usable.
I have the latest drivers for the UD-ULTCDL, XPS13 chipset. I don’t want to extend the monitor since this will be very confusing for my wife, who is technophobic and having trouble getting used to Windows 10, never mind using the screen differently!
Sorry to hear about this issue. I’d be happy to try and assist, though to the best of my understanding this is a Windows scaling issue and would likely happen even when directly connecting the monitor to the XPS or other host computer.
My general recommendation in cases like this is to have suggest manually lowering the resolution of the internal laptop display to match that of the external display (or to get it as close as possible) and then set the scaling to 100% on both displays. Once done, Windows should never try to scale the displays and you hopefully won’t run into the issue anymore. It’s not ideal, but it should work.
If I set the scaling on the XPS13 to 100% icons and text will be too tiny to read.
Either Windows or the UD-ULTCDL driver obviously detects when the 1920x1080 screen is connected and adjusts the scaling to 100%, it’s a shame it doesn’t work the other way around i.e. when the screen is disconnected.
Unfortunately there’s no real perfect solution at this time. You could try significantly lowering the resolution of the XPS screen, but that would probably make it somewhat to mostly unusable.
We run into this issue quite often with most of the current ultrabooks on the market. The small physical size screens with extremely high resolutions cause terrible DPI scaling issues with external screens in docking scenarios.
We’re hoping that these behaviors improve with updates to Windows in the future.