What you describe is something the game inherited from its X-Com roots; in some scenarios enemies are just placed randomly all over the map, roaming until they see something to attack, or see their allies being attacked. Enemies have limited vision just as Battle Brothers do, and unlike for the player, their individual vision isn’t aggregated into vision for the whole group. This pushes gameplay slightly more towards careful advancement and exploration. On the other hand, in the “Defend the Hill” and “Line Battle” scenarios all enemies know of your position and will attack in concert, which puts an immediate focus on fighting it out.
Both feel slightly different to play, and we’ll probably have both in the final game, weighting more towards battles that play out like in the “Line Battle” scenario, with two armies directly opposing each other once they engage on the worldmap. Certain battle conditions, however, like attacking a bandit camp or arriving late to defend a town that is being raided, would have enemies more randomly placed around the map, without every single enemy being aware of your presence from the start. We’ll try to find a good balance for the final game.