Online Table Extents 2

This is a follow up to my earlier post regarding online table extents. On doing some more searching in the manuals, I found the oncheck command. Running oncheck -pt for the tables mentioned in earlier post shows that the first extent is 30 pages, next extent 15 pages. This is half of what I specified in create database statement ( create table extent size 60 next size 30). Any enlightment would be appreciated.