Well, I'm a n00b here, so take anything I say with a grain of salt, but... well, all the short stories I've drafted (not many) I didn't go out of my way to make complex or simple or anything else.
I just thought of the story I wanted to tell. In one case it's a fairly simple short story about a boy who attends a funeral and learns he's the only one who can see the ghost. It goes into a little detail about it but in general it's straightforward because it didn't need to be complex.
Another short story I had an idea for was multi-layered and extremely complex. The character was many things at once, the worldbuilding was fairly complex for a short story, and there were several themes running throughout it... not because I wanted to make it complex, but because the story in my mind was complex.
Neither story is all that great, honestly, but those were my thoughts.