I checked it on my Krogan Sentinel and same thing. Tech Armour was reducing the damage by the full 50%. My first thought it "awesome, Collectors are bugged to suffer our full DR". Then I tested it on the Geth. Same result.
After testing some more the new formula for enemy damage that I came up with is:
((enemy_damage * difficulty_modifier) * cover_bonus) - (enemy_damage * difficulty_modifiers * DR) = final_damage
The difficulty_modifier for each difficulty is:
Bronze: 1.25x
Silver: 1.9x
Gold: 2.5x
Platinum: 3x
cover_bonus is either 1 if you are in cover, or 1.4 if you aren't.
Basically what I found is that damage reduction does not affect the enemy's "out of cover" damage bonus, but it does affect the rest of the damage by the amount listed. This means if you are in cover then you do in fact get the full damage reduction amount.
Admittedly this doesn't change things around a lot, except that being out of cover means you really need 140% DR rather than the previously believed 134%and being in cover means that your damage reduction is just as effective as it says it is.
So in general:
> Being out of cover means your DR is ~71.4% as effective as it says
> Being in cover means your DR is 100% as effective as it says
Edited by Cyonan, 26 January 2013 - 08:22 PM.