They're still new, they need time to settle and get comfortable. That being said, you don't really get polys for activity.
If you want activity get a Sen or a Polli and that's your best bet. Otherwise you just have to like the looks of the fish and you may luck out and get an active one. My Del was only active in random spurts.
I think that cover gives them security, and I like providing that for my fish. But if you provide too much they can have a tendency to hide too much, too - depends on the fish.
If I were to do it again, I'd do floating plants and/or maybe pothos or whatnot set up top with roots growing down into the water. I'd also maybe do a couple of red lotus which don't take up much floor space but give overhead cover.
I'd provide some wood/branches that were more in the water colum or even coming down from the surface and try to keep the substrate as open as I could. For me since I like natural looking tanks best, it would be a way to make it look like the edge of a river/lake, but still be able to see the polys (on the substrate) and give them some security.