Ways of Limiting Birds Eye View
Given that all board and miniature games are inherently flawed because a player can see everything -when the desire is to have a sense of realism for what commanders could actually know and see- there are only a few practical ways it can be implemented for fog of war and birds eye view effect:
All components (brigades at the minimum) of a force must have an objective, else they are on "hold," or else immobile and in "reserve," until a senior officer activates them by personally moving to the hex next to a leading unit of the group, or that groups commander who is in proximity of the group of units in question.
All arriving forces must have a stated objective point to reach and that location can only be changed by the senior commander sending a physical miniature courier figure -regardless if that courier is bearing any actual written order in secret or not- to the recipient's neighboring hex. Obviously if the objective or location cannot be achieved the recipient force stops, deploys for defense and waits for further orders.
Arriving at road forks/intersections: randomly roll to see which road is taken (other than backwards).