...I used a GeoTagger to add a field GeoFenceNames containing the names of each GeoFence the received event's Geometry is INSIDE as a List. Note that I did not use the default DelimitedValue. If the received event's Geometry is within an area overlapped by two GeoFences, the List appended to the event by the GeoTagger will have GeoFence names at the first two index positions: GeoFenceNames[0] and GeoFenceNames[1]. (Note that the list's index is zero-based.)
By sending the geotagged event through a series of Field Calculator and Field Enricher processors, I can isolate the individual GeoFence names from the list and use those individual names as the key to the join needed to further enrich the events with attributes from a uniquely named polygon feature.