I have these on my single tier rig, and the shutter plate was key. There are 2 vents on the burner, and I actually put foil tape over one entire vent, then rotated the plate to cover up about half the other one. That gives me my optimum flame; your optimum probably depends on both vent size and on the propane pressure the burner is receiving. With both vents mostly open, the flame would blow itself out. With both of them mostly covered, it burned yellow.