The maximum excursion capability of a driver is dependent on the design of its voice coil, magnet structure, spider, and surround, and has (pretty much) nothing to do with the enclosure. This is the parameter referred to as "X-max" in the driver's Thiele-Small parameters.
But the extent to which a given amount of input power at a given frequency produces a corresponding cone deflection (and SPL output) is of course highly dependent on the enclosure and port tuning.
But the extent to which a given amount of input power at a given frequency produces a corresponding cone deflection (and SPL output) is of course highly dependent on the enclosure and port tuning.