An interesting experiment would be to place an upward growing coral (acro, monti digi) below the direct flow path and allow it to grow upward into that strong flow. See what you get. I would think the growing tips would slow their upward growth and start to thicken up to be able to take the flow.
Another interesting option would be something like a monti cap placed just outside that heavy flow and seeing how it reacts as it grows outward into that 6" space. Again, I would think the piece would thicken considerably as it grows to be able to withstand that type of flow. Something to think about.
Scroll corals also strike me as good for such places. Hard, thick growth should fare well under intense flow. They just look like they're built to take it.
Bill