I haven't done a compression tests in more years than I can remember, 20 yrs+
I do remember doing them both cold and hot and adding oil into the weak cylinders to see if that helped the rings seal better, if it didn't increase more than a little bit I was taught it was not the rings leaking, it was usually the valve train causing those issues.
Using a leak down meter you can feel the air leaking around the rings by blocking off one breather and holding your hand over the other one to see if it builds pressure up in the crankcase or not and you can hear it leak by the valves on the carb side and the exhaust sides if it is bad valve sealing
I do use a brass hammer to pop open the valves when doing a leak down test that I hear leakage from the valves, sometimes it will help and on others not very much
I use them as tools to help me under stand what condition the heads, blocks and rings are in