I found that when I moved the mic around the room I had results that were in correlation to the standing waves that are found in that room. If I moved the mic a foot or two closer or further from the center I would be able to get the flat responce I was looking for. When you get to the point where you think you need to stack frequencies try moving the mic around a little and see if it makes a difference for you.

Standing Waves in Room

Trivia: I belch at around 125 Hz