quick question, can you not leave them outside to flower?.....that would really be the best for the plants. but if i had to bring them in, depending on size i would probably flower them with the 400. since the suns light cycle is not 24/7 here if you were to bring them back in and put them in 24/7 it could shock and stress your plants, it could work but the chance of them becoming hermies are more likely. and as for how close the light should be, as close as possible without the tops burning, just put your hand under the light and lower your hand until it doesnt burn it....that should be alright for your plants. good luck