The 'thrust puck' the engine is mounted to is designed for multiple engines, none of which are in the centre. They are only using one engine this test, but are

The 'thrust puck' the engine is mounted to is designed for multiple engines, none of which are in the centre. They are only using one engine this test, but are testing the flight-design thrust puck (as opposed to some interim structure with a centre mount for the single engine).