Fair call.
Until I had seen that forum I had never heard of that technique to clear a plug - beats destroying a good propellor for nothing.
As for how it works I am unsure. By cycling the prop at those mid-range RPM's you still gain a fair wad of extra Manifold Pressure, effectively I would think, increasing the volumetric flow through that or those cylinders - if more air or in this case charge is entering the cylinder then I gather that the operating pressure would be higher at the power stroke. Maybe this technique "mimics" higher operating pressures and temperatures by cycling the prop at lower RPM's. I'd like to find out more though if anyone has any ideas?