Meh I gave up trying to work this **** out last world..
I tend to go for piles spaced 6 tiles apart, on farmed land.. 4 piles in a row.. 1 100%, 1 x 2 moldy boards, 1 50/50 ish, and 1 x 2 dry boards only.
there was no real pattern, I wasnt online when they matured and no forageables spawn in that area (as it is farmed)