For me, I used a couple layers of tarp each covering the entire area under the pool. I believe Intex says not to use sand as it can wash away. I did use sand contained in a level ring made of that black, tubular landscape edging. I checked for level, added sand and re-graded each year when I assembled the pool. If you don't have a way to contain the sand, stick with the compacted soil - the sand will wash away if it can. Also, I would avoid putting the metal frame parts on sand, the sand will let then sink right through.

Sorry for questioning your level - but... (as I'm sure you know) - to many (many many) people 2" across 18' would look perfect.

Another thought. If you're considering sand for a better feel under foot, you might consider foam - 1/4" closed cell foam in rolls is available from Internet pool supply places. Tape the seams and put it under your tarps. We put up a small (10') donut on my parents irregular (but pretty flat) concrete drive and first laid down the styrofoam insulation you'd use under vinyl siding. It worked well for protecting the pool bottom and for a slight cushion.