Deciding where the Wagner Tuba players should sit is not a straight forward matter!
With the Wagner Tubas needing to join with the bass tuba at some point in a 5 tuba ensemble, the normal seating arrangement for the 5 instruments is not ideal. So, either the bass tuba player has to move from his normal position near the trombones to sit near the 5th-8th horn players or the horn players have to move across to sit with the bass tuba player within the ‘heavy brass’ section.
Neither option is ideal and so you never quite know where to look for the players at an orchestral performance where Wagner Tubas are used.