Actually the settings were not solely introduced due to the varying sensivity over different missions. In some they were super sensitive, in others they were almost deaf. This is due to mission authors sticking to the default acuity settings despite the fact that different level architecture leads to different average distances between player and ai. The majority of the team members back then however decided it should be up the players to make those adjustments. It might be used for other purposes now, but that was not the intention.
That is indeed a bug then. Will look into it.
That's odd. The calculations performed to determine whether the indication animation should be played and the ones performed when actually performing the blackjack are the same. I'll look into it.
You misunderstood the point I was trying to make. Knocking out ai is a fundamental gameplay aspect. It might be true that performing this is more challenging in TDM than it was in Thief, but it should still be possible. That you have to alter gameplay settings for this to work is not desireable.
(I'll see if I can dig up the discussion, as it's been a few years.)
EDIT: I've corrected my statement regarding the acuity sliders. I couldn't find the discussion regarding the ai too sensitive vs. ai too dumb, but I know we had it once (caused by a review of TDM). Another thread was about that it is too easy to kill ai, another that the ai could be more challenging.
It all boils down to that TDM was designed as a more challenging experience, but as this caused the game to take more time for unexperienced players to get into it, the idea arose that it would be great to have dozens of different difficulty sliders. The major issue with blackjacking though was that players have problems with properly hitting the enemy, not necessarely with them beeing to sensitive. So although those settings obviously affect blackjacking, too, that's not the main reason for them to be introduced.
None of this is relevant here, though, as the changes made do not affect the acuity. So whether or not you are able to approach the ai is untouched by this, but what happens once you try to take them out is what should have changed.
If you perform a blackjack attack said attack should succeed if all conditions are met (as far as judgeable by the player). It shouldn't fail because you hit a part of the body you wasn't even aiming for.
The blackjack should not get hung up on level geometry that isn't even in you field of view during your attack or only at the edge of the screen (the typical ceiling beam issue).
The indication is for new players to help them get a feeling on when a blackjack attempt should work. I guess experienced players would turn it of either way. We have to see whether we get it to work in a relyable way. If it is causing more confusion then aid it can be removed (it's only an extra, nothing that needs to be added).