I just picked up a used set of these for my '99 Civic Si, and the top of the spring is a lot smaller than the seat it is supposed to go into in my upper mount. Shouldn't it seat on my polyurethane seat insert? It looks like it would go right inside that and just sit on the metal inside the upper mount. What's to stop it from moving around inside the seat when I am driving it? Is there supposed to be another piece on top of the spring?