(A suspicion of mine is that each mob in a group has a slightly different skill level. You will get an easy one that goes down fast, you will get a hard one that resists, dodges and is generally a pain to kill. This does seem more natural although it's probably impossible to verify this. To rule out this effect from averaging calculations you'd need to make sure you killed the whole herd yourself and killed multiple herds. Other unknowns are the time of day, whether the creature has just been sleeping or eating or maybe even had a fight (and recovered all HP of course). We just don't know how complicated it is and we did learn recently (at the IRL) that some of the mob AI is turned off atm.
Random occurances tend to cluster I think so you do get bad runs of dodges for example.
We also know that you get diminishing returns for things like parry mods. My guess is that the difference between your level+parry mod and the creature's level+parry mod gives 10% more chance to parry for a difference of 20. I.e. the 10% figure and +20 max parry mod in the patch notes. A previous Q&A addressed a similar issue, if I ever get round to finding it I'll quote it.
A few well formed questions in this month's Q&A could clarify a few things. I'm happy with a vague understanding or even a popular misconception as long as it prevents everyone running around with the same equipment made from the same mats
)
