Stock cam 360 idles bad, dies in gear, fixed!

Then we agree that lifter preload cn make a difference. However, the way you describe it, is that the preload makes a difference in this "Idle" problem when it doesn't. DGC333 is correct, you are partialy correct.

Your ignoring the way the lifter is made to operate.

At low RPM, this preload issue is not an issue unless grossly out of wack. The lifter has approx. - .100 total travel. The first and last .010 are not useable. (Give and take on that. Also, I would not run preload down to the last .010)
So, this gives approx. .080 useable adjustment in order to set up the engine correctly.

Moving the pushrod up high or down low in the plungers travel has an effect of the performance of the engine, but not at idle.

DGC333 is correct.