When I use Solo cups, I use 3 cups per seedling.... maybe I over think this shit, but there's method to my madness....
one cup with a load of holes on the bottom, thats the usual but then I cut the botttoms out of 2 more cups and stack them so that the seedling cup is raised off the ground.
I found that just having one cup I had a tendency not to drain properly - the cup sits in a film of water that stops full drainage from the cup.
Plus having 3 layers of plastic makes me feel better about reducing light getting to the roots.