I think people are too hung up on numbers....
I have used Sterilite tubs for incubation for years - more often than not, they're tubs that had snakes in them at one time (so they have ventilation holes). I have never measured humidity in an egg box, or within my incubators. Funny thing is, the eggs hatch (the good ones, anyway)
I've fooled around with a variety of substrates - vermiculite, perlite, sphagnum (long strand), potting soil, peat moss, and combinations of the above. The eggs hatched.
I use vermiculite, rarely mixed with perlite, these days - but that's just personal preference, and not based on results. (peat moss and potting soil are essentially dirt, and are accordingly messy; I usually can't find long strand sphagnum in quantity....and perlite just sticks to everything).
Dave and Tracy Barker said in one of their books that consistency is more important than specific numbers with regard to moisture content and humidity. Eggs can hatch in drier (or wetter) than ideal conditions; but don't decide halfway through incubation to change things.
I know the thought process is to optimize everything....and it probably does improve results in some cases...but I can't bring myself to approach it like a science project.