Any formula will have to be based on some shot trajectory. Higher shooting clubs will need less thought about it. Imagine how the ballistic curves look like when the target ground moves up or down.
With the Starters many pins weren't accessible, elevated greens needed a lot of extra length, one or even two clubs.
Today, with the new G20s, I usually don't add much or even no length but I won't let it one foot short and I know that backspin shortens the shots.
Therefore, you are back to educated guesses...