This doesn't seem to work for me. I applied the 1440 regedit, then set in-game resolution to 1080p, but it still just changes my monitor to be 1080p when the game starts.
registry entries set what the game needs to be stretched to (which would be your monitor resolution), for things to get scaled, you need to set in-game resolution smaller to your monitor. To do that, you might need to make a custom resolution in your graphics card settings. Keep in mind that this only affects in-game resolution
Also, 1080p stretching to 1440p is not 2x
quarter of 1080p is 960x540 (you need to create a custom resolution of 960x540)
quarter of 1440p is 720p
quarter of 4k is 1080p