Oh, it looks like we are going the same direction with attempting a low-light moss wall! I look forward to the updates on how it fills out.
But I think that moss walls usually tend to grow out instead of across (in between the mesh). You best bet would be to trim it back periodically, and then maybe insert the clippings into the mesh to try to spread it out more evenly if you want a thick wall, rather than just growing out into the tank.
I might be wrong, though. Honestly, I am just starting myself.