Fragmentation and Extent Size

I just today started playing with 7.10.UC1 (Solaris 2.4), so this may be an easy question. I dbimported a database exported from 5.05, and then fragmented a few large tables by expression over 6 volumes/dbspaces. the tables in their source dbspace consumed about 45Mbytes of space. In the target dbspaces they consumed over 700 Mbytes. Very Strange. I snooped around a little and found that in each of the fragments, huge initial extents were allocated, and then only a small portion (7-10%) was actually used, accounting for all of that growth in allocated pages. Anybody care to speculate on why this happened??? I set the index fillfactor to 80%, so that would account for a little growth, but not that much. Otherwise, I'm not sportin' a clue. thanks in advance y'all... greg