I think position 1 needs to be more west or southwest.
Settling on position 1 on the screenshot will lose 3 grassland tiles inward our territory. We lose 2 tiles near river (2 grasslands with forest - its easy to notice) and a tile 4 moves south of position 1. If we could move city only 1 tile to W we would catch them all.
Its too much space to waste. Notice that there is no enough space to squeeze there another city which might use those tiles.
Position 2 seems ok. We can't avoid jungle.
Position 3 could be great place to settle but we need to explore the area. Pos 3 will have few desert tiles if we settle right at the place. And there could be some goodies south in unexplored area or at least grasslands.
Conclusion

: pos 1 to move W or S, pos 2 is ok, pos 3 needs exploration.
Good job blackheart!