Actually the opposite is true.
TC makes you harder to detect in terms of game coding. Although this may not be noticeable within the game.
Lets use Aircraft as an example:
At 1xTC patrolling aircraft follow a precise course with active sensors covering every degree of their sensor arc. The AC also travel ALL of their allotted course. So AC travel to A > B > C > D > E
At +512xTC aircraft still follow a precise course BUT 'jump' certain distances at predefined intervals while doing this their sensors still cover the same detection arc BUT they are less likely to 'spot' you. So in this instance AC travel A > C > E, skipping point B & D, very handy if you are at point B/D.
The same is true of all 'AI' within the game.
So to the OP's question, it may seem that you are detected easier/sooner while submerged but the game does not work that way coding wise. It is just a trick of the mind as time is passing faster leaving you less time to react to or correct your actions.
Clear as Mud? I thought so.