Make them optional.

Seriously I read all this words about immersivity and so on the I read complains like this.

Just make some web search about snipers and height, or think about history and middle age castles and how they have turrets to fire arrows to the invading forces. How can any one says that there is no advantage with heights or disadvantage being downside a enemy?

To me is obvious. From a higher point I almost have a better field vision while the enemy will have difficulties in locating my position, projectiles will have a slight more speed of impact cause of the difference of height, while those thrown from below will have a slightly less speed of impact (these are basic physic knowledge).

Thus again how does height doesn't add as advantage factor?