I think that you can keep water level all the way to the top, but i think that u need to put there only low light plants. I don't think that light go down to botom of aquarium, especially because now you have a lots of plant on the top.
This is low light plants that i recomend down in aquarium monoselenium, cladophora, anubia i cryptocoryne
I am not expert, but this is what i have learnd
I have in my riparium Iris plant (blue and yelow) acutualy only one week, but it start growing, temerature is 22 degrece, no co2, just treset and osmokot.
I also put pontederia.But highest level in my aq is 34cm, and i have now only at 25, but evry 3 days i put 10 l of water more.