I think I have come across a weird bug that I could not find in my google searches.
When I am aiming with a ranged character if I point the cursor at the enemies' feet, I can get higher ground bonuses from a higher ground but if I aim at their head I do not get any bonuses depending on the distance.
Also at the barn love-making fight, if you aim at the half ogre's head from specific distances(not exactly sure how far) you will get lower ground disadvantage but you won't if you aim at its feet. I think this happens because the aim calculator works with the distance pointed not how far the character is as a whole.
So it seems like shooting feet is the best way to aim to me which makes no sense. It would be cool if it did less damage but more accurate. But right now there is no penalty to aim at their feet.