More grain = higher strike temperature required.
Higher ambient temperature = lower strike temperature required.
Yesterday my numbers were a little off on strike (too high - ambient temperature threw me off), but I always have a half gallon of both boiling and cold water to make adjustments. I add it in eighths of a gallon, check again, add more if necessary.
Really though, you just have to learn your system. I suspect more like one year rather than ten...