Yeah I certainly have nulls as well as peaks. The left speaker is a lot different to the right in the Arc display due to me having to take the door off so I could get my desk in lol.
I took 30 measurements on that graph moving roughly a 1/2 foot either side of the central spot and 1/2 foot forwarda and half a foot back from the central spot and everywhere inbetween.
I'll take a Soundforge sine sweep tomorow and record with Arc on and Arc off into cubase then take a look at the plot afterwards. I'll do 1/2 ft either side of the seet spot but I rarely move either side when mixing.
I took an older video of my room when showing proof that you could run a HZ/Volts Yamaha CS-30 over CV from a Motu Soundcard... so you might be able to get a rough idea on the size of my room if that helps.
YouTube - Yamaha CS 30 running Silent Way in Cubase 5