Ok, thanks for giving it some deeper testing.
Its interesting to see, that you got totally different stamina reg increases than me.
As i wrote i just wanted to check out my highest possible stamina reg with the build i wanna use after 1.6 hits live.
And with 6 Medium Armor Parts + Werewolf my stamina reg increase after using a Potion is exactly 20% (as it should be) and the increase after killing an enemy is nowhere near 20%...but it should have been 30%...
Maybe the passive is beeing calculated with your base stamina reg value (without gear etc) that could explain it, but if this is working as intended is another question...