I took a couple of SPL measurements using Avia warble sweep and LFE sweep. According to Avia the phase switch should be set where the SPL meter maintains it's highest reading. On the warble sweep with the phase switch at zero my meter dips down to about 68hz at two different points during the warble sweep, once at about 78hz and once at about 67hz. With the phase switch at 180 the dip stays higher (aroud 72hz). I get a similar 4db difference in the LFE sweep. My sub is in a corner on the same side of the room as my mains. My understanding is that the sub phase switch normally is set to zero if it is placed in the same part of the room as the mains. But from my SPL readings it looks like 180 is where I should set mine. Am I interpreting these results correctly?