Yes, updating it would be fine if you have tested those values and determined that in your case they are ideal numbers. If you change lenses, focal lengths, or cameras, I think it's better to look into the FWHMSigma, FWHMMedian, etc. values so that you could use the same expression for any case. That'd make the expression relative to the data-set instead of fixed values, though, so it's more like "best of this batch" and not "best ever".