What you call the "top plate" has been traditionally called the subchassis. If you're as old as I am you'll remember a number of audio terms that have lost over the years. The one that drives me nuts is when people refer to RCA jacks as "ports"... as if it were a computer.
I replaced a set of new springs and my top plate won't center (line up when viewed from the top). I can twist it by hand and rotate it back square with the plinth and chasis but after it bounces a few times goes back to being off. What could it be ? I don't think it's detrimental to the sound as nothing is contacting and it's floating. it just looks strange