i see. just make sure that each boostee has a linked counterpart and you can boost them with any high level you wish.

linked counterpart means...
they're RAF linked.
they're within 4 levels of each other.
they're in the same party.

if you meet all those requirements, you'll get 3x exp no matter who else is in the party doing the boosting.
remember though, you get the most experience the closer you get to the suggested level for the instance. for example, i remember getting a good amount of exp at level 30 in SM graveyard but just a little bit more in library/armor and cath. but as i near 40, my exp gains were growing a lot more in armory/cath (about double) since my characters were closer to the suggested levels for those instances.