"I think I understand what you mean. Your thinking that when the motor heats up, the pushrods expands, and this would make the adjustment tighter correct? Well..everything expands and grows not just the pushrods, the rocker arms, the heads, the pistons, the bores, the rings..everything. The heat excites the molecules causeing them to move. Just like airing up a tire..You add molucules they bump into each other, they have now where to go, they expand the tire..It heats the tire up also...."

See this is where I get into trouble explaining it. They say "Well if the pushrod is expanding and getting larger and the roller tip is expanding then the lash will become smaller(tighter) as the two metals "grow' towards one another as they expand!!!
Mike