a bit of personal experience here with above.
What I have noticed is that when using a 'dense' wood lump charcoal ( high carbon content) it's better to bury the wood chunk under the charcoal so atleast it gets consistant contact with embers. ( I have recent experience with Iron bark charcoal sourced locally from Victoria , Aus and it hardly had good embers on the surface level at 250F . So all the wood chunks I threw on top resulted in white smoke which smelled like lot of creosote. And turned to a piece of lump charcoal rather than burning into ash ). If the fire was at 350F this is not a problem as I had embers visible on the top of the charcoal heap.
But with medium density charcoal, I found to have slightly more open vent settings and embers visible from the top even at 250F when the deflector plates are taken off. So the smoking wood pieces eventually give a cleaner smoke even when thrown on top of the charcoal.