I was wondering if the little fold-down focusing aid was really the optimum distance for my material so I set about making a set of gauges to measure the distance between the material and the underside of the laser nozzle. I then cut a test piece at a number of heights to find out which was actually best for cutting my 3mm acrylic. The photos below show the depth gauges and the results of the experiment.
You can see that 12mm and 11mm seemed to give the best result. I therefore made a setting gauge 11.5mm high and am finding that gives more consistent results than using the fold-down device.