So, the problem has been with the AVANT since the tube was replaced and I am assuming the problem did not exist with the old tube before it blew or may be you did not notice.
Given what you say, the most likely cause of the problem is going to be with the scanning assembly which sits on the neck of the tube and magnetically deflects the tube beams or the service engineer failed to correctly set the Horizontal Centre Switch marked in the service manual as 5S1 and can be found in location 7E. This is a physical multi position switch and nothing to do with the software setting via the service menu.
I am assuming you are not a technical person who could investigate this yourself, so I suggest you call in the B&O service department again and direct them to the above switch adjustment.