While cleaning my room i got an idea
What about to make a formula for stun chance related to target's STR combined with IF and dmg recived and maybe total hp?
If you will take a IF an STR as modifiers you can do something like that:
Stun rezistance chance= [Hp-(Hp-dmg/Hp)]+[(STR+IF*1.5)/100]
Where first square brackets is dmg recived and next one is modifier you have from combo of your str and if. Keeping that in 0.XX will be easy to use in othet things if needed, easy to change into %.
1.5 number is a number showing how much IF is worth looking for stun possibility
Only thing you will need to set are levels of stun you can set in table or in easy if... then formula
Sorry, i'm not a programmer, but i think this idea could be nice.
I'm not even a item ballancing advise club, but maybe you will have a look at my idea ;)
It could be funny to see in this game a full plate full str guys like butan that are running aroud and laughting because arrows are thickling him but not stunning (at least those from weaker bows)