One inch is just a ball park figure. There are so many factors involved it is impossible to say for sure what is safe and what is not. A one inch drop at one post could do terrible things to a pool where a gradual three inch drop from one side to the other might be just fine. It also depends on the amount of dirt backfilled around the outside of the pool. A pool one foot in the ground could easily be six inches out of level and be just fine.

Dennis