Using Excel, dosing Flourish trace, Flourish Iron, and dosing Nitrogen to 15ppm, with 2wpg lights I have moss growing in plague proportions.
One small palm sized bunch of java moss grew enough to cover a 60x30cm tank and was 10-15cms high in only 6 weeks.
One thing to remember in growing a wall is that all of the moss needs light. If you only place one light above it, then only the top will grow because the bottom part of the wall will be shaded.
For it to look more dense it is a good idea to keep trimming the moss flat, this will encourage the moss to grow more shoots.