So I messed around with the githyanki patrol fight yesterday. It started when my Ranger wanted to finish off that boss lady ( forgot her name ) and I found that I had a hit chance of only 55%.
It wa even ground, clear LoS, with Lae-zel standing slightly to the left, and another Githyanki slightly to the right.
I saved at that point and started moving around to see how I could increase my hit chance. As long as I stayed on the even ground, I couldn't increase it. I could easily decrease it, if I moved too closed. It then dropped to 30%.
I finally moved up that little hill. It's only a couple of meters. Halfway up I was still at 55%, but as soon as I reached the top, I got to 80%, so I finally felt good to release my shot and kill the boss lady.
Thoughts about that:
The change in the hit chance I noticed is massive. From 30% while standing even slightly too close to 80 % less than 10 meters away with slight elevation. Is that really workng as intended? Even the 25 point swing from even ground to slightly elevated seems way too large. THat is a whopping 45% increase in my hit chance.
Secondly, I have no clue about 5e rules. So I have no idea why my hit chance was so low, or why hit chances generally seem to change at random. To be honest, I just want to play the game. So the fact that I felt compelled to check this out, because it is never explained, and because the swings are so massive, suggests to me that something is broken here.
Just to make it clear: This is not a complaint that there is a change in your hit chance. I am absolutely in favor of positional modifiers. But the changes are in my eyes ludicrously large - I would go with a swing of 5 to 10 points in either direction. It is no wonder that every mob is trying to get to higher ground.
It just beggars the question why we don't carry stepladders around...
