dbimport and size of rootdbs

Hi all! I have a problem that I believe is to do with extent sizes but I can't put my finger on the cause. I hope one of you can advise me: I have a system with lots of dbspaces, some with multiple chunks. I have another system with exactly the same dbspace/chunk configuration. I took a dbexport of a database on system A (using -ss flag) and then dbimported it onto system B. It failed because I ran out of space in the rootdbs. System A has only sysmaster, sysutils and my other database. System B has only sysmaster and sysutils. I am running Informix 7.23 on AIX 4.2.1 (not that I think it matters). Why is my dbimport using around twice the amount of space in the target rootdbs compared to the source rootdbs? Dan