Ok, here we go. I used Thunder Clap for the testing since it hits for the same every time(more or less) and it has a shorter CD than CB and Shockwave. Before I started testing I tried doing Thunder Claps on a friend to make sure I had the formula correct(since I know his armor). My testing shows me that a boss dummy has 11 621 Armor. This is the specc I used:
Talent Calculator - World of Warcraft Damage formula for Thunder Clap:
(Basedmg+AP*APcoeff) * Defstance * Mitigation * imp. TC * 1h-spec.
(300+AP*0,12) * 0,95 * Mitigation * 1,3 * 1,1
Armor formula:
Armor/(Armor+400+85*(Target level+4,5*(Target level-59)))
ArP Cap formula:
This is where our formulas differ:
WarTotems formula:
MIN((Armor+400+85*Target level+4,5*85*(Target level-59))/3;Armor)
Rashors formula:
MIN(((Armor*(1-0,04*Sunders))+400+85*Target level+4,5*85*(Target level-59))/3;Armor*(1-0,04*Sunders))
Where "Sunders" is the number of sunders on the target. The difference is that my formula reduces the ArP cap aswell when you put up sunders(and buffs that reduces armor by a %).
So the actual armor with my formula will be:
Armor*(1-0,04*Sunders) - ARPrating/1400 * MIN(((Armor*(1-0,04*Sunders))+400+85*Target level+4,5*85*(Target level-59))/3;Armor*(1-0,04*Sunders))
Which is then inserted in the Armor Formula and you get the mitigation that is used in the Thunder Clap formula.
I got the "Actual DMG" from doing 10 Thunder Claps with each setup and then took the average value.
The only case where our values should differ is with both Sunders and ArP Rating and as you can see my model is more exact. On a sidenote: If your model was correct that would mean that it would be possible to reduce the armor by more than 100%, in theory. I'm a bit tired so please check it for errors.