I have a three sensor setup and it's working really well. I probably don't need to do #4 but I was curious about a possible configuration. My question specifically is the placement of the 4th sensor:
Right now I have a rectangular room with two sensors on the front wall and one sensor behind and to the left. If you stand in the center of the play area with 12 noon directly forward, my sensors are at approximately 10 and 2 with 5' between them. The third sensor is behind and to the left in the corner, let's say at 7.
Finally, the question! Must I place the fourth sensor in the other corner? Or can I place it to my right say at the 3 o'clock position?
On a piece of paper draw a rectangle the shape of your room. Draw three dots at the positions of your sensors. Next, draw a cone starting from each sensor. Look at the diagram and ask yourself two questions: which area of my room has not been covered by my three sensors? Where do I put the fourth sensor to cover the uncovered?
I'm sticking with three - I may try to mount them a bit higher and see if it improves things, but I have to be honest... except for some very slight issues right at floor level (i.e. picking up a dropped weapon in Dead and Buried) it's been fantastic.