It makes a lot of sense that the tightest wick would be most consistent, but I was wondering if you had tried testing this way. I'm sure there will be some that decide to try a tighter wick made with #500 and it will be no better for them than before because they hold their PV horizontal and have found a good balance.
Again you answer yourself, if you have found a good balance, use it. Good balance are hard to repeat and gravitational flow has more variables than capillary flow. So i believe in "kiss". No need to test. If the 500 is excellent in the vertical the very little gravitational force it would receive in the horizontal is irrelevant. As you go to other looser mesh and larger holes the gravitational becomes more relevant and even necessary to adequately feed the coil. Now we would have to calculate each degree over horizontal because the higher you tip the unit the more flow, the level of the fluid in the tank greatly effects the gravitational flow. So personally I would rather have a wick that only counts on true wicking.