I believe the float keeps it upright but unless the inside jets are creating enough flow, its not going to be as effective in sucking itself down to the floor.
One additional thing to try other than looking at the float is to remove the filter bag and see what it does. If the bag is not providing enough flow, the venturi effect will not be as strong.
When I had a DE leak, the DE was clogging up the inside of my bag and my 280 was very lethargic.