Sometimes you cant hit an enemy with a ranged attack because there's something in the way blocking the path.
You need to move a bit to a spot from which the line of attack would be clear.
But, when looking at the battlefield from above, it's hard to judge if you'd be able to target the enemy from some new position.
Currently the only way to make sure is to move there, and then you cant undo it....
What they implemented in Solasta, was that as you mouse over positions to move your character, it shows arcs for attacks from these positions to all nearby enemies, so as you mouse over planning your move, you're informed that from the position you're considering, some target would be hittable.
I miss this feature when playing bg.