Adobe Photpshop is coded to handle High-Resolution DPI. It does not use Windows scaling. Adobe Photoshop UI scaling currently is a Global setting for Photoshop UI and only offers 100% or 200% scaling of all Displays. If you wish to use windows scaling. Windows will scale all that Photoshop Displays UI and Image. With Windows 10 it easy to do using a Windows Shortcut setting. Change Application handle High DIP to System Enhanced. Set Photoshop CC scaling to 100% if yuo use Windows scaling....
Put the whole application on the 24" screen, with all the panels and tools. Set 100 or 200% as appropriate.
Then drag an image over on the 27". Close it again. From now on, all images should open on that screen. Image scaling is independent from UI scaling, so the scaling factor is moot here.
At least that's how it worked last time I used multiple monitors.
1 person found this helpful
That is the best way to deal with High-resolution displays these days. Use multiple displays with different resolution. For example do not use CC 2xUI scaling and keep Photoshop UI on your low-resolution display and edit your images in floating windows on your High-resolution display. The only Photoshop UI info in your High-resolution display will be the information in the floating image windows frame and image rulers. Look at these two screen captures and a picture of my displays two 20" 100Dpi flanking a middle 24" 4k 185dpi display. Adobe is working on an improving Photoshop UI scaling feature. Some day it may be useable on very High-resolution displays.