Isn't the EA area basically the tutorial + first area of first act? DOS2 also only really opens up in the second part of the first act, and later even furthermore.
I
think the EA will turn out to be the entire first act, between Larian stating that the game will cap out a couple of levels beyond 10 and the world map that popped up a while ago. Already there's more than four levels' worth of XP in the EA and as you can see on the map, it spans all of the locations highlighted on the right-hand side.
So, assuming a three acts structure, my expectation is that you'll have a first one from the Nautiloid to Baldur's Gate, mostly covered by what's in the EA, a somewhat longer second act in the city itself, and then a third chapter set somewhere in the planes.