Not all locks were built the same !
The 'draw' of the top end paddle is dependant on where the culvert enters the lock
On the Trent and Mersey Canal (Cheshire locks), the water enters the chamber from under the cill directly down the chamber so putting water under the boat and drawing forward to the cill
On the northern section of the Starford Canal, the water enters the chamber just in front of the cill but at right angles so boats are pushed away from the bump board/cill
I have not seen the Tardibigge chambers drained, however, they will be a variation of the above which will result in a pull of water towards the cill