Looking at your pictures I suspect the turf material you have applied might be a bit thin. Can you apply the material a bit thicker to allow moss to get a faster chance to take hold. I know moss will grow on anything if the conditions are right but I suspect it would do better on a thicker surface. Also being thicker it would hold more moister, that helps with the plants and keeps the humidity higher longer between misting.

In the two builds I made with peat most covering the background I obtained different thicknesses. On the 55 gallon I did I used Gorilla Glue over foam with peat moss and it holds great, bit harder surface and seems thinner then the one I did with silicone. That one I applied a heavy coat of brown silicone over foam and packed handfuls of peat into it. Once the silicone had dried I brushed and vacuumed off the excess. The remaining peat surface felt softer and thicker.

In any case don't give up as each time we build one we learn a great deal.