I presented a model that allows an estimate of particle numbers to be made using simple arithmetic. For the model spheres were assumed, not irregular particles. For identical spheres 225 is correct for square packing. Hence we have a ball-park figure of 2475 particles for 11 fields. For actual AWS 17 particles the number will obviously be different - as you have pointed out. It will not, however, be way out. With a maximum of 2 unacceptable particles being allowed that will correspond to 'less than one in a thousand'.
