Eraldos test was a good start. Sounds like he didn't get any help from the factory on the subject. As the old every reaction has an equal and opposite reaction holds, I'd like to see another study of the phenomena with high speed photography.
As the opener clobbers the valve it is accelerated downwards where it contacts the closer. Which boots it back up against the opener. Repeat this X times for each valve excursion. Then the valve gets the seat bounce and radial stem wiggle before it settles down for the compression cycle. There is a lot of violent physics at work here!
I 'm not going to provide the tight clearance test mule but my logic follows that if there is a couple thousandths clearance when the engine is cold and a couple thousandths when hot that all would be good. As an engineering study one would keep reducing clearances until something got damaged. Rockers and cam scuffing or other maladies. Then open clearances until reliability is insured. Hmm, maybe that .004" is correct.
Until I can measure hot clearance I would logically assume that clearances will change when hot as there is a lot of physical distance of aluminum between the valve seat and the cam bearings. Considering this, perhaps closers will tighten a bit and openers slightly less as the aluminum expands.
Aluminum expands .000023 mm per degree Celsius depending on the alloy. A 1 meter bar will grow 2.3 mm if its temperature increases 100 degrees C.
Something fun to watch. The mass off the valve spring knocks the valve around quite a bit. Desmos have the bounce between openers and closers.
YouTube - Valvespring at 7000 RPM