Same boat as you. Here is what we did. Excavator got to within an inch. From there you need not worry about the entire plane of the pool. Just make sure the rail itself is all sitting on the same plane the entire perimeter of the pool. We used a water level and set all our pavers for under each rail. We are plus minus an 1/8 inch on the pavers the entire way around. (O.K. we are a bit anal) We then set the rail and ensured it sat on dirt the whole way around. Once the rail was set you can use the sand to ensure the center of the pool meets your specs. Keep in mind that optimally you will have a two inch sand base so you can make up the variances in the center of the pool with that. Just make sure that rail is level for now.