Normally, if you select “play in standalone game” with -fullscreen command added, that will ignore higher resolutions than the native one of your screen.
But there is a way to bypass that 
just set a high resolution, like 3840*2160 for standalone windows size, and immediately after you launch the “play → standalone game” function, just click on an actor, or every other thing to gain focus on the editor while the standalone vertion is launching, and it will launch it on a reduced process, just click on that process, and it will launch the standalone game with native downsampling processed
Since I’m supposed to ask a question, I’ll ask this : why we have to do this ? it’s cool that it works that way but how/why ?