There's about 3 watts per gallon so lighting is more than enough...but I think the key is really the bioload from the fish...i torn down a 24 gal nano plant tank and the black sand/carribea sand mixture was like mud as i scooped it out, smelled like it too if not worse. the plants in that tank grew like there's no tomorrow.
this red sea max 34 gal has more light and the bioload is alot higher plus I dose excel and flourish regularly. Anubius tends to be a slow grower but i see new leaves and or sprouts every week. The substrate in this tank is also pretty old so i'm sure alot of crap (literally) is in it, making it a nice rich feast for the roots of the plants...