The pool should be built on level, undisturbed soil. Dig enough to sink the patio blocks (under the verticals) so thier tops are flush with the soil. Spread a sand bottom inside the pool after the walls are up (put the sand inside before you raise the wall). If I were doing it adain, I'd install foam cove (in addition to sand bottom) becuase the installer who built my pool did an inconsistent job with the sand cove and now (two years later) I'm worried about one section of the pool where I can see the bottom rail against the liner.
I have 1/4" closed cell foam on top of the sand bottom and on the walls. It makes the walls soft to the touch - the weight od the water has compressed the florr foam so there's no appreciable feel to it. I don't know about 1.5" foam bottom - never seen the material but it sounds like it should be enough to protect the liner from any bumps / rocks in the soil base.
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