How long has this been in the tank? Mine required 3 weeks to produce foam, then it immediately went into overdrive. Don't mess with the settings, leave the water outlet and air intake flow valves at their most open position, then don't mess with it at all, it will require time to start foaming. I have run mine at all different levels of water in the sump, doesn't make an appreciable difference on the amount of foam produced, it's always the same at any level.
Also remember, any time you stick your hands in the tank, add an additive, feed your fish, or mess with the water in any way; the skimmer will respond by not producing foam for a short time.