I often see it mentioned that the selection of the launch site for Ariane 6 was one of the preliminary requirements that froze its final design. That does make sense, especially since there was some disagreement between DLR and CNES whether Ariane 6 should have a solid fueled first two stages or not, with solid core likely leaving less of a leaway in launcher's configurations, depending on which launch site it would operate from.
The launch site selected was, expectedly so, French Guiana and a new launch pad will be build for this carrier rocket in the Guiana Space Centre, Kourou. What I didn't find anywhere is however which other launch sites were considered for this, now with finalized preliminary design, ESA's next generation launcher? So to my question:
Which other launch sites (except Kourou) were considered by ESA for Ariane 6, and what arguments eventually tipped the scale in favor of Kourou?