Yes, the caliper pistons will "flop" some inside the bores. There are springs on the backside of the pistons, to hold a small amount of pressure on the pads, to keep them close/touching the rotors at all times. The overall diameter of the pistons is such that only the area that holds the actual seals is even close to the diameter of the piston bore. The areas ahead of, and behind the seals is quite smaller in diameter, unlike most caliper pistons, which are a fairly uniform diameter all the way down.
You don't have a "problem", as far as that goes....that's the way they are made.
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Joel Adams
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