Danny,
Sorry, I should have made clear that my Sea Vixen ball was in a straight tube not curved, and worked perfectly when turned 180 degrees as in inverted flight. Maybe 'flight' is the wrong word for an inverted TM which descends like a brick, but it showed me the need for full right rudder to counteract the windmilling prop, and almost full forward stick to maintain nose-high attitude in the glide.
Desmond my instructor reluctantly agreed that it was difficult to fly by the seat of one's pants when one's backside was half an inch off the seat no matter how tight the straps. It was good training for later graduation to Stampe and Zlin with their inverted fuel systems.