I found that when using test signals standing waves are much more noticeable. In my case in the mid-band moving my head from side to side made a dramatic change in the level. It's quite likely that the meter is reading correctly and your ears are hearing correctly, it's just that they are in different locations! With respect to the RS meter being inaccurate, yes it is but more so in the lower regions. In the mid-band its within a dB or so, close enough for what you're using it for. Rives does make a test CD that corrects for the meter if you don't want to do the math yourself.