BTW, I've confirmed that the second Irradiance Cache is the reciprocal of max error by setting max error explicitly to 0.025 (2.5%) via Python, as Stewer described, and the slider appeared set to 97.5.

Oh, phutz, I can't calculate this morning - too little sleep. Anyway, 0.025 does map to 97.5. Somebody awake please work out the formula.

Whichway