Simple answer )...... Ya do the hand test... You put your hand at the level of the top of your plant and you set your light to it..... if your hand burns, your light is too low.... heh
General rule of thumb is no closer than 18-24 inches for a 400 watt light.... I am not sure on a 1K, but I would not get closer than about 30 inches or so.... Your lights are vented though, so you might be able to get a LOT closer. Use the hand test, it is good.... also whenever you move your light, watch your plant the next few hours for signs of overheating.