Defense acuity works a great deal less often than the other forms of defenses. It works at about 1/10th the effectiveness as the others at around 2.5 % Center of being had the greatest effect on this however. In the following test the defense acuity went off at about roughly 20% or so with Center of Being up.
Ok, I did some more fighting, logging and counting. All against Giant Sandbeetles. All hits taken without CoB were in melee, some of the hits taken with CoB were at range, so that skews the hit/miss ratio somewhat due to my less than stellar ranged defense:
Without CoB: Attacks: 442 Hits: 290 Misses: 141 Evade: 3 Block: 3 Counterattack: 5 65.61 % hits, 31.90 % misses, 2.49 % E/D/C With CoB: Attacks: 442 Hits: 204 Misses: 145 Evade: 38 Block: 28 Counterattack: 27 46.15 % hits, 32.81 % misses, 21.04 % E/D/C
Without Center, 11 out of 301 hits are evaded/blocked/counterattacked. With Center, 93 out of 297 hits are evaded/blocked/counterattacked.
Again, those are numbers from still minor sample, but I'll keep adding.