Posted flow rates you find on websites are a generalization. Flow in an SPS tank is critical to keep clean water pushing in and around the colony which keeps crud from settleing within it. But there are variables even with this.
Let's say you have 2 seperate tanks. Everything identical between them except that one is stocked only with softball size birdnest corals and the other is stocked with Acro or staghorn type corals with a large diameter branch. The tank with the birdsnest is going to need a much, much higher flow throughout as they grow in such a tight form and they create turbulence within themselves that restricts water movement inside the tight branched colony. The other thick branched SPS tank could withstand a much lower flow as the water is less restricted getting through and around it. I'm not trying to imply that you can slap an MJ1200 on a couple of thick branched acros and be fine.
There's probably a much easier way to explain it than what I just did but I hope it gives you an idea of what I'm trying to say about the variable factors of flow "requirements".
