? on archives and ontape

Hello friends, I have observed some archive behavior that I don't understand. Perhaps someone can shed some light on this. I have 2 identical systems - same hardware, o/s, and Informix release - IBM 720 running Sun Solaris for Intel release 2.4 with Informix 7.20.UC2. I make an archive on box A - it is just over 12 mb in size. I restore that archive to box B. Everything is fine. I am using ontape. But if I turn around immediately and perform an archive on box B, the archive size is just over 4 mb. Now I know that an archive is a binary image, so no reorganizing is being done when I restore to box B. After reading all that I could find about archives, the only thing that I thought might influence the difference in sizes is the logical logs. The oldest log with uncommitted transactions and any logs following that one are included in the archive. But I don't have any open transactions on either box during the archives. Any ideas? Thanks, Mike Ballentine