Try a card under, then the 1/8" homosote, then shot, then thin card over shot.
Some guys, in cylinder bores, shoot a couple thin "B" wads over the powder, then shot then 1 thin card. They figure the thin, light over-shot cards
lack the weight and energy to disrupt the shot cloud like heavier wads do. Photos prove heavy wads blast into the rear of the shot cloud which causes huge holes in patterns - 1910 by W.W. Greener.