Is there any consideration in your math for the fact that the target is three levels higher?
For example, Actual miss chance is 5% - 0.6% = 4.4%. The boss only does 100% of their attacks, they don't attack you 102.4% of the number of swings they have in that time. This applies to all the avoidance factors. Since the actual number of attacks is set to 100%, the avoidance factors have to account for the target level and be shifted to the 100% scale.
So out of 195 swings, and 4.4% of them miss, that's 8.58 misses over the course of the fight (naturally a "partial" miss can't actually occur).
Also since your calculations of how much of each avoidance doesn't include level scaling they are in the wrong porportion. Because the 0.6% decrease has a greater impact on Miss which only had 5% to begin with relative to the same 0.6% decrease to something like Parry that was over 12%.
Total actual avoidance if factors are...
Miss = 5 - 0.6 = 4.4%
Parry = 12.59 - 0.6 = 11.99%
Dodge = 10.46 - 0.6 = 9.86%
Avoidance = 4.4 + 11.99 + 9.86 = 26.25% (you're math resulted in 28.05%)
26.25% of 195 attacks is 51.1875 avoided attacks (again can't "partially" avoid so this would be rounded).
The percentage of attacks avoided that would be missed is...
4.4 / 26.25 = 16.76% (you're math came up with 17.83%)
All of this math needs to be converted to a 100% scale cause there are errors all the way through if you think the boss makes 102.4% of their total number of attacks.
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