Rolling 2d20 in a vacuum is different that rolling 2d20 in DnD or Baldur's Gate 3. You can take out a pen and paper, start rolling and track the delta between the rolls, and the average will trend to a number between 3 and 4.
That being said, the thread has been more focused on the total impact/value of higher ground giving a character advantage, while incoming attacks roll with disadvantage. With collision detection and other factors, high ground has other benefits alone that can't be measured.
