Upper levels really don't count for square footage if you don't have the bottom level the right size.
It would help because the top two would have above the recommended space, and the bottom three would have the recommended space. I'm guessing you have your cozies/kitchen on the top floor - if they chose to all run laps on the bottom floor at the same time, it wouldn't be big enough. If anything, though, the ramp actually takes away a bit of space, unless it's external.
I've seen how your cage is in the closet (which is a brilliant idea, by the way) - could you possibly make your cage a 3x4? It wouldn't be as long, but it would stick out a bit more. 3x4 is the same as a 2x6, so you could fit five sows in there if you really wanted to. Or, since you are hoping to adopt this new girl, you could stack it (like you have right now, just a dif. size) and have three on the bottom and three on the top, and it would be even bigger than a 2x5 - and def. bigger than having five sows in two stacked 2x5s, together.