Hi Christopher,
In order to license a Lpar with AIX I used sysamcap PARTITION in order to get the exact number of cores you should license. You can find sysamcap utility at $SYBASE/SYSAM-2_0/bin/.
Check that output it should recommmend you 4 cores if you have an entitled capacity of 4 and a capped lpar.
Hope helps.
Javier.