When creating a new profile, the first thing that I do is add a citation and associated abstract for each of the sources that I have at the time. By doing this, I ensure that I'm only creating sourced profiles. When I subsequently compose and make updates to the Biography and/or Research Notes, I leave the source reference definitions where I initially created them (in the abstracts).
In order to keep a source reference definition in the physically first occurrence of each source reference, I'd likely have to move each source reference definition multiple times, as I'm developing the bio and notes, each time potentially introducing errors. Additional benefits (just my opinion) of leaving the source reference definitions in the abstracts are that it reduces clutter in the actual bio and notes, and groups all the source reference definitions in the same place.