From my post here:
http://www.dual-boxing.com/showthrea...229#post199229

I have tested this out level by level.

If the linked characters are 3 levels or less difference from each other they will both get RAF bonus as long as the kill isn't gray to either.
If they are more than 3 levels apart the LOWER level character only will get RAF bonus as long as the kill isn't gray to the higher level character.
This also applies to quest RAF xp bonus. As long as the quest isn't gray to the higher level character the lower level will get the bonus regardless of the level difference.

An example of a test I personally did was take an 80 unlinked with a lvl 20 linked with a lvl 40 to SM. The lvl 20 received 3x XP with RAF and the lvl 45 received 2x XP with rest until it ran out then it was 1x XP.
I'm betting what you were killing was gray level to your level 16.