Napther Yup, I've already noticed that problem (ie. be inactive for a few days and when you come back, your FPs are so far in the negative side that it's nearly impossible to get back reasonable values).
Imo, faction points plummeting when you're inactive is fine (so I'd like to avoid decreasing the normal decay), the real problem is the absence of a lower bound (I said earlier I'd like to write a script to reset the FPs to more reasonable values, I haven't done it yet but I'd like to do it soon).
48h before being labeled as inactive might also be too low, I'll increase the delay to a week (168h) and see if it helps.
(I've just resetted your FPs to 100)