As long as you are in the stroke of the lifter piston the amount of preload is not going to impact the idle. A lot of preload can cause issues with lifter pump up at high rpm.
I'm sorry, but you're just flat out wrong here. You go tryin to tell this to anyone who has ever run a hydraulic cam with adjustable rockers. You can taylor the valve adjustment on a hydraulic lifter very much in the same way that you can with a soild. In some instances, it makes more of a difference than differing the adjustment of a solid. It all depends on the cam grind. With your logic, you're saying that an engine will run the same with .020" preload as it will with .060". Go get a .040" feeler gauge and look at it. Are you really saying that here? Sorry, but you're WRONG.