Oversized scaling of RStudio on UHD monitor using Windows 10

I have a Surface Pro connected to a Dell U2715H monitor, which is 2560x1440 resolution. On the Surface Pro, RStudio scales very small, but that has been noted elsewhere and is adequately fixed by changing the zoom to 120%. However, if I transfer the window to my external monitor everything but the menus are oversized.

There is no workaround for this issue that I've been able to find. Any suggestions?