What brand /model is it?Yes that's right, lap restraint across the seat with the large belt wrapping around the back. Honestly we've really tried with it with all the logical ways and there's nothing we can do to get it to fit. The buckles in my car are recessed within the seat whereas on other cars they've been free on the seats in the back -- this would make a difference.
I suppose it depends how far the back of the seat extends outwards. It touches the back of the passenger seat which I don't imagine the belly of a 25 st. person would do, but of course they would be wider than the seat is deep. I don't know why it seems such an awkward seat but it is!