On: Dell Ultra Sharp 24" 4K display

[sliverstorm]

This monitor doesn't support scaling. If you push 1080p, it will not fill the screen.

[jfb → sliverstorm]

That's not what HiDPI mode does; rather than rely on the (uniformly crappy) on-board scaling logic on the display, the computer sends a full resolution picture that it has scaled already. And there's no reason to think that this won't be available with this display.