PortLime's Buccaneers now has True Start Locations for YnAMP.
Each leaders has a seperate start location Bart Roberts starting in the Caribbean (the actual island of Saint Barthelemy does not appear on the map so they start on the Brittish Virgin Isles) and Henry Avery starting position on Madagascar (the island of Île Sainte-Marie does not appear on any of the TSL maps so they will spawn on Andrangazaha as it is the closest city to the island).
Big shout out to Port Lime for letting me make this and to the folk at the Civ 6 Modding Helpline Discord who helped me as a fresh set of eyes.