That could be one reason why they dont move as much. The purpose of a ported box is to control the amount of excursion while increasing the output around the tuning frequency of the box. But there could be another reason that im not thinking of.
i've got L5's, they dont have all that much excursion available to them either...the square design doesnt allow for much but they give good loud bass off because then can move a good amount of air with the excursion they have available to them...
what size l7's are they? I have a 15 and it has 3.5" of excursion. ofcourse I'm throwin 1100 rms to it.