If you want you moss wall to grow out faster, try thinning the moss out a bit more to the point that no frond overlaps another. From the looks of it, you should be able to spread out what you have to cover practically the 2 plates you are using. This will maximize your moss, allowing all the tips to get enough light. right now, everything you have that is being shaded will not grow as fast (if at all) and is essentially wasted.
As for your H.difformis, you might want to think about swapping some with a grass type plant like c. helferi, Vallineria, Sagitteria, crinum, even narrow leaved forms of Echinodorus (E. uruguayensis, horemanni, narrow leaf red rubin etc.) I have always liked the use of vertical lines in a tank that has Nymphaea, makes for a great counterpoint to the big wide lilly leaves.