I have a britax b dual and have had the car seat on the bottom until recently. But when i have had the car seat on top the harness adjustor strap hits my bigger one in the face. When I bought it (second hand) the lady handed me a bit of lycra with zips on and said something about it going on the underside of the car seat. Can anyone tell me how to fit it or even what its called so i can try to look it up? Thanks