I would like to know any experiences with using 580EX Master on camera hotshoe, a 580EX off camera as Slave in group B, and a 580EX as Slave in group C in the outdoors with sun. Are there any difficulties in getting both remote flashes to fire? Must there be direct line of sight with photosensors of A-B and A-C? Or can slaves B & C read the flash coding fired by Master A reflected off objects like the ground?