how close can my light be?

I have a 1000 watt hps over a 4x6 flood table with 30 plants on a light track. My temps are perfect. How close should I have this light?

I noticed some leaf cupping and twisted growth. . . . .

Min 18" probably more like 36" if bulb is not in a cool tube try to check temp on tops of plants cupping usally is heat stress got a good fan for air circulation not just ventilation? raise it 6" if it keeps up just my 2 cents

picture will help 3 feet

Like this


or this


or this

Is that a 1000 watt? Are you cooling it? My bulb is in a reflector with glass, usually air cooled with a 6" duct/fan. Right now it's cool due to winter weather conditions and ducting is not necessary.