Go look up the info on rubbers and plastics. And if you do remove a rubber cone the will (eventually) return to their unloaded state. Likewise they need time to get to their operating position/compression.
Chris should be along soon to explain.
I think you've captured it well enough there, Nick.
Theoretically Steel Springs should never sag, until they are stressed, then they will change shape, however, there's inevitably impurities in Spring Steel and so these too will 'sag' or 'settle' over time.
Rubber isn't a spring, but does have great elastic properties as well as self damping (shock absorber) qualities. Because of this type of combination if elastic and damping qualities, it's spring rate never actually stabilises. That might take a bit to digest.
Putting it another way, if we say compress a block of rubber in short time (say less than 5 - 10 seconds) by 1" and we measure a 'rate' of say 100 lb, that's 100 lb/in, however, if you leave it compressed, the rate reduces after about 1 minute, this will be around 90 lb for the same 1". After about 5 minutes, this will become 70lb and so on it goes in an exponential curve. If you left it for say 24 hrs, it would possibly come down to 50 or 60 lb. It does seem to reach a 'plateau' point, where it's rate still does change, but at snail's pace, it's at this point where the suspension in our Minis (and Mokes 
) we feel has 'settled'. Even then, as we know, while it may take years, the spring rate is still creeping down, along with the ride height.
To a point, Rubber also has a Memory (it is said to be 'plastic') and so if maintained within it's Plastic range when the load is taken off the Rubber, it will (eventually) return to it's molded shape / size. Rubber also never fully cures either, it continues to get 'hard' with age.
