Right, the plate adjusts how much air gets into "B" along with your propane. You have the positive force of the propane shooting down "B", it can't magically come back the other way against that pressure with nothing pushing it from that side. Your reg is 10-20 psi os force "pushing" the propane down the tube.
With that plate off, you're simply getting much oxygen into the mix.
Put the plate one, Light burner, adjust plate until you have Blue flame with the slightest yellow/orange tip. You don't want big orange flames.
You want #4, not #1