I'm not sure, that was just me hypothesising out loud! Though it seems plausible judging by (potentially) various comments and from the map itself: there seems to be coastline around most of it except for where it meets Luculla to the north. It's not certain of the dark forest and Teneb Tiriel are one and the same, again that's just hypothesis, though I personally think it's a fairly compelling idea.
I guess it really depends on whether or not Larian view our adventures on Rivellon as taking place in one cohesive area or whether they're only tangentially connected facets that could be geographically distributed all over the world. Since a lot of what we see is quite ancient (even D:OS being pretty ancient history compared to much of the rest of Divinity has its own ancient ruins and legends) there's a reasonable case for the latter, but I prefer the idea of a smaller, more easily mappable region.
Of course D:OS2 brings in a whole bunch of entirely new regions which could be absolutely anywhere. Part of me thinks Fort Joy could be near Sentinel Island but then again it could just as easily be on the other side of the world. My (possibly incorrect) impression is that they may focus more on game lore this time around, but whether or not that will include any commitment to Rivellon's geography is anyone's guess. Doesn't stop us speculating, though, in which case I've decided that Fort Joy is part of the same archipelago that includes Sentinel Island. So there.
