I think the problem with your seats is you have that extra padding that prevents it from folding further down. Even with the original seat covers it never goes completely flat it sits up at probably a 10-15° angle. Until you put something on top of it.
Peter would know for sure, I am sure he has transported all sorts of things in the back on his numerous trips.
Peter would know for sure, I am sure he has transported all sorts of things in the back on his numerous trips.