I imagine a spot centered between both lungs directly below the spine. Then I visualize the angle the arrow must follow to bisect that spot. On level ground the arrow follows the same elevation from entry to exit through that spot. From a tree stand the arrow must enter higher and exit lower than that spot depending on the relative elevation to garantee getting both lungs . I also do it on quartering shots entering and exiting either in front or behind relative to the spot between the lungs. I have found my impact point is slightly higher for a given range when shooting down as opposed to level ground so I normally put my pin on the same spot whether level or not unless it' s an extreme downward angle that I have to adjust for. Hope this helps.
TJ