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....

When pressure goes up so does temp they are proportional. As pressure goes down so does temp. This is why those old Deodorant cans get real could when you use them for a few seconds. This is actually the basic principle of how a A/C unit works.