Key there is to set your bar height to agree with your flexibility. If you watch pros, they literally melt to the handlebar in that position. There isn't any tension and its a pretty secure position. If you lack flexibility and your bar is placed too low, this will be an awkward if not unsafe position.
Lack of flexibility creates too much tension if trying to ride in too low a position which affects not only power production but unsafe steering.
If you want to confirm this, raise your handlebar with a riser stem and then try the TT position.
Hope this makes sense.