Your post in ICloud and DOpus - #6 by AlbusD indicates iCloud isn't really a drive, just a folder below C:\, so it'd fall under the usual drag & drop rules ("move when same", by default).
You can customize what happens when you drag & drop things by editing Settings > File Types > All Files And Folders > Events > Drag-and-Drop; however, making decisions based on the destination folder (rather than the source) would probably require a little scripting.
(Personally, I find it easier to not have to think about the relationship between source & destination folders when dragging things around, and I change the event to always move (Copy MOVE
), then hold Ctrl down when I want to copy things instead.)