A hydraulic lifter does not "bleed off as it rises to open the valve. The plunger does not move in the lifter. It is forced to stay in one position because it is setting on a locked (due to internal valve) hydraulic column. As soon as the lifter moves up, the valve moves up. "0" lash. The lifter plunger keeps moving in its bore only to take up wear. It will move only till it reaches the snap ring.

There is usually more than !/4" travel in the Small block Chevy lifter. So if you set the lifter plunger at the bottom of its travel, you would have adjustment ofr 1/4" of wear before things get noisy. But, no room for expansion of metals at operating temp. That is why the plunger is usually set about mid travel and higher for hi-perf use. This allows the lifter to adjust to the proper "0" lash.

A hydraulic lifter will not over fill or "pump up" during normal operating use. Only when rpm gets high and valve springs are weak will the lifter "pump up" and hold the valve open..

Even then the lifter is not actually pumping up from oil pressure. It is merely adjusting to the increased lash caused by the lifters not following the cam, pushrods doing the Hula and the valve springs bouncing around. Thats why when the rpm comes down, the lifters go back to working like before, to the original setting, as they only maintain "0" lash.