As shooters we all reason and apply logic to our process and what we have experienced. The best advice is to try it. Something in the 0.001 to 0.005 inch will work. It may not work for the reason we think and it may not work in every situation and with every powder. There are some very complex interactions with bullet retention and combustion. I am not able to explain how it all works together..... so I test and learn.
Huh. Figured it'd be reasonable to set to -0.002 and go with it. Though, as you say, the chemistries of powers can vary, and each barrel+bullet combination will have slight differences, so I guess it doesn't surprise me that variations in neck tension might prove preferable in a given setup.
Have the Redding Type S F/L sizing die, with several of the neck bushings. On the 0.292" measured seated rounds, I'm currently using the 0.290" bushing but can vary from -0.001" to -0.004" (0.291" to 0.288" bushings).
Having just recently gotten back into reloading, I'm measuring most everything. Every round. Overkill, probably, but it's helping me to see what the tools are doing, what my technique's doing, what the gun's doing. Ending up with pretty consistent dimensions on the cartridges, too.