Xmech (maximum mechanical excursion) on the highest excursion woofers I know of is around 60mm. That is 30mm from the resting position or 1".
John. I thought you had to worry about compression if your driver is too close to another large object like a wall. The rule of thumb seems to be that if you locate two subs within a quarter wave Lent of each other you get the maximum gain (~6db) from co-location. This would suggest that a few inches would not make an appreciable difference.
On the other hand, if you put two EP800s about a foot apart facing each other, there should be just enough room for your head and maximum pressurization at the ears.
