I followed manufacturers instructions and let mattress sit on a flat surface for over the recommended 72 hours.  I am a small active person with average weight and after less than a week of sleeping on the bed I was experiencing a lot of low back pain.  There is a clear center lag in the mattress.  The picture shows a straight edge that doesn’t go all the way to the ends,   but clearly shows the center lag.  The edges are much higher than the center.  Maybe I received a defective mattress.  Cudos to Denise at Wayfair who heard my complaint and made sure this was rectified and very quickly!  Will be a loyal customer of Wayfair.