I don't for sure about each species of fish on my list, but I would imagine they would swim through the grasses, like any other structure. There will be some that hang near the top, some mid-water and some on the bottom.
I am very particular about assembling a harmonious community of fish. If any fish doesn't get along, I have no problem removing it. I do not get attached to any favorite fish. No one species is more important than the whole. For me, it's not a box of pets, it's an ecosystem in a box.
So, one way or another, I will have a harmonious community of fish, thriving in as complete an ecosystem as possible.