When I made mine I just played with the angle until it worked before I screwed it together. Its not that severe but I could not tell you the actual angle. I know I was going to get you pics i forgot, its hard to show well because its all assembled and the only good pic would be from the outside. I use dense commercial carpet squares, its not fluffy at all so the eggs roll well. I would think fake grass would work, just test the angel with an egg and the grass in place before screwing it in. If you start this way they will never know its "supposed" to have nesting material. Before they were laying I would carefully place wood eggs so they would not roll out, of course I was putting them back all the time because they would knock them around and they rolled out.
Gary