Same here. With 17 feet and the hole 1 inch lower than where my ball is, on a straight line to the hole, I use 16 feet as the distance to the hole. If the ball was 2" lower I would use 15 feet as the distance to the hole. If the hole was 2" higher than my ball I would use 19 feet as the distance to the hole.
I want the ball to have enough pace such that it would go 2 feet past the hole if I miss.
An exception is when there is a lot of break. The ball will have to roll farther so a bit more power is needed to get to the hole.
Note: I use somewhat less stroke power for downhill putts than I would for an equal length putt that was uphill.