consider next extent sizes which may be larger chunks in oracle than in your WANG envoionment. If a next extent is requested the default chunk is allocated , and for the current final extent it may be nearly empty ... and what are your settings for pctincrease?
You can check the highwater mark in the tables to see the unused space
Attached is a script that I use ... Change the OWNER in the script and
run from sqlplus ... It will show the total space and the unused space for
all tables with a size > 1meg ... (dbms_output.put_line) ...
This can easily be modified to do the same for indexes within a schema also...
Also check out your pctfree & pctused (only for tables) as these can dramatically alter storage requirements. Indexes can be shrunk with the compress clause sometimes as can tables though you may have adverse affects if you dont test it properly.
I would still run the scripts to see what the size was (if I really wanted to know what the differences was) ... As well as checking pctfree as AlanP stated... If pctfree =40, then Oracle is only going to load data in 60% of a given datablock leaving the additional 40 percent for DML. I don't have
a clue as to how WANG manages their datablocks, but if they fill them, then
pctfree is probably your biggest reason