So far, working on a rough base outline like yams farms with the center being tilled, having at least 8 tilled blocks, 3 sand and 3 water, surrounding that central one, all within a 7x7 cross and diagonal connections…
the picture will help.
I did a bit of messing with the combustion fraction. Using the same shape, I placed a metamorphic stone in the middle, and planted the seed.
8 gravel max around it, more is not added to any calcs, zero other stone within the area, and max of 3 lava blocks (1 source, 2 flowing is fine), seems to give me a 0.460 seed-chance, and 0.650 yield-chance. 100.0% growth scale is accomplished simply by removing all stone and placing in anything other than stone, or leaving it air)
I’ve tried soils, stones, sand, those boulders, all 5 types, on the same level as the seed, and the same level as the ground it’s planet on, light level seems to make zero difference, light sources nor full daylight.
Are people managing to find other modifiers?
Spitterlizer doesn’t add to the figures, just thought I’d quickly try that