Where I have it, it is a Dwarf sweet flag in between big rocks, doing quite well for itself, the shelf is deep around 20 inches, but it's a dwarf one. I do have a regular one but it's foliage died quite rapidly back in autumn so it's not woken up yet.
In the bog I currently have bogbean, carex riparia, yellow flag, juncus. I recently added bog bean and yellow flag, I also have one I put as a marginal in pond. Very interested in tropicals when it heats up a bit, as those are something else. But perhaps I already have enough bog plants as I hear when it gets going with spring, the bog can go crazy especially with all the nutrients.
I am interested in trying non conventional plants, like Hostas, and I also hear Astilbe. One thing I do regret is not having a bog area built into the pond that acts like a natural bog where soil/gravel is always wet but there's no standing water.
I also added a fern around 2 weeks ago to the pond, two lemon button ferns and one regular fern. So far so good, I didn't submerge the rhizomes but ferns can take some time to respond though.