Putting green firmness and OM2

How much does putting green firmness change for every unit change in OM2? That is, when total organic material at the 0 to 2 cm depth (OM2) goes from 5% to 6%, or vice versa, what type of change in firmness can you expect?

From my measurements, I've found the relationship between OM2 and firmness goes something like this.

When OM2 increases, greens get softer. When OM2 decreases, greens get firmer.

For the "how much does firmness change" part, that…