Cage size and suitability really depends on the personalities of the piggies to a certain extent. I do see the point that size recommendations are based on one floor, because at times all pigs will be on one floor and they need to be able to move around and scoot about without getting under each others feet. However, not all pigs like to scoot around, and not all pigs feel the need to follow each other around all day as a herd. Everyone's herd dynamics will be different so I can only speak for mine, but mine (when I had a herd) utilised all levels of their cage and could be found on separate levels as often as they could be found together. I honestly do find that having different levels is very good for a herd, and even though they don't officially count for floor space (and the reason for this is logical and sound) piggies often genuinely do find that being able to access levels adds to their enjoyment of their living quarters, and it really can aid in making a harmonious environment. Like I say though, it will depend on the dynamics of your particular herd
There are clever things that can be done to maximise the floor space whilst still providing enrichment. One is to create fleece forests - you can shape these as tunnels but they can also run in and out through any part of it as the fleece forest dangles from the roof, not going up from the floor. You can, for example, have one floor as a hay loft, but also place hay racks on the sides of the others, so they can move to different areas and still access hay without having to be on one floor to do so.
One thing that a lot of people do is to make a run that fixes to the bottom level, assuming the cage rests on the floor, and for a while they can come and go, I do this for mine, and I promise you I have a very small living room with four people 16+ sharing the one small room (the kids don't use their rooms much), but it works because it's not a permanent feature and can be removed when you need the floor space.
Several of things you can do, IF you do end up feeling like your pigs may like more room.
For a pair of piggies, it's likely that they'll be perfectly happy in there