Not sure you have the height for 50 watts, might be a bit too intense, guess we'll find out...
Am at 30 watts and 16 inch height with Vero 18s, you might need more distance.
Running veg with Vero 13s at 350mA, so low they don't even warm up heatsinks, working on jumping up to 700mA with them and should be about right. They are 24 inches from floor, soil line is about 6 inches high, leaving plants a foot in which to grow and be trained. They like it, but feel it would be even better with the higher current eventually.