yes and in my calculations i assumed a raid setup where i would always have 20% armor pen from jugg or similar debuff.

so thats the reason for 1- (0.2 + aditional pen)

is it wrong ?

edit: not sure why yours is hiting that low. i am sure that without armor pen the formula above holds true .. so 35% is the actual dummy armor. i have picked up the formula from this thread .. so ..