A lot of the ABV increase is based on what initial charge is used in the thumpers.
Water= Less flavor, lower ABV
Wash= More flavor, slight increase in ABV
1st run strip= slight loss of flavor, higher ABV
It is the very things that we think we know, that keep us from learning what we should know.
Valved Reflux, 3"x54" Bok 'mini', 2 liebig based pots and the 'Blockhead' 60K btu propane heat