Btw, it takes like couple of mins for the wave pattern to form properly every time u adjust the power.. So adjust, relax, see and adjust again if necessary...
My tank is 2.5ft w 1 inch of sand, i place the wp40 on the overflow wall abt 1/3 the way down from the surface... meaning that the distance btw the wp40 and the facing wall is less then 1.5ft, slightly tilted to bounce of back wall of tank...
Hope it helps