The wallet is about .75" thick. If the picture I attached works you should be able to see slight evidence of where i tried to mark my phone number. The horizontal one should have been between the blue dashes, the angled one centered between the blue dots.
It is possible it was too low. I was doing different sized pieces and I never got an alarm until I tried a 3/4" piece of wood, at which point it told me 1/2" thick max with the tray and 1.5"-2" without the tray.
It seems odd there is a 1" gap there where nothing would technically work properly without a gap. I guess people just use wood blocks or something to stack it to within the proper distance from the laser?