Two DMR moisture figures circulate and growers mix them up. The manual says good synthetic long method compost should hold 68 to 72 percent moisture at spawning. The same manual describes compost after Phase II as 64 to 66 percent. Both are DMR figures and both are correct, because they describe different compost.
So name your compost before you name your target. Above 72 percent, DMR warns that aeration fails, conditions turn airless and plaster moulds appear. NHB links compost below 64 percent, with wet casing, to weeper mushrooms. Neither end is small.