On the current version of ECS, the Avoidance % on ECS is .6% off of what it actually is.
After digging through Defense.lua and reading it, it appears its caused by "enemyAttackRating = (UnitLevel("player") + 3) * 5" on line 69. I can see why this was done, but its also inconsistent.

For every level above you that a monster is, your chance to be missed, dodged, blocked, or parried is reduced by 0.2%. So, for a boss, which is 3 levels above you, its each of those reduced by 0.6%. You changed the Miss to adjust for Bosses, but not the others.

For fixing this, I would recommend just removing the +3 from that line. Most tanks (and Tanking WAs) consider avoidance cap as 102.4%, to consider the .6% reduction for all 4 of those stats. making them all fall in line under the assumption of your enemy being a boss would make it more confusing overall.

Also, this was difficult to figure out why, but Crit Reduction from Resilience is incorrect. I believe Wrath changed the crit reduction per point of Resilience. The best fix for this is to change line 44 in Defense.lua to "local critReducingFromResilience = GetCombatRatingBonus(15)" 15 is the combat rating number tied to the Resilience stat, and this has the advantage being more accurate at any level instead of calculation crit reduction per resilience at max level.

Hey @LordOfOtakus thanks a lot for taking such a detailed investigation of the tanking stats! I'll try to dig into it myself and push a fix for it as soon as I can ❤️