I have seen several air boxes begin to shrink up. (usually the single filter box
on the exhaust manifold side of the engine style.) The ones on top of the motor seem to fair better. I have seen them squeeze in around 3-6mm on some cars. (high engine heat) The air filters have also seemingly gotten bigger. They may be trying to compensate for the fact that once the filter media in the paper filters gets damp or wet, then dries. They shrink down a little.
Some of those filters in c280's and older e320's can be a real pain to get in there correctly.
Dr.D