Which position can you install a capsule in, i.e. centre, left, right? Are there legal requirements?

The lady at the shop told me Im only allowed to have it on the left or in the centre.

I will have a maxi rider in that car for DS as well, and that would mean he'd have to get out on the right side (i.e. the road side) of the car becuase he wont be able to get past the capsule.

I had thought I could have him nest to the door and the capsul in the middle or right side, as it will be easy enoughto get the capsule out over the maxi.