Distance a 1k can be from the top of the plants

My area is a 4X5 and I have a 1000K MH cooled by an 8 inch sunleaves fan. Currently the lamp with a Sunleaves 8 inch air cooled hood/and glass panel is about 4 foot from the base of my drain tray. I kinda want to set my lamp hieght and forget about it because I will be LST and only growing 9 under the hood. What is the maximum distance I can put the hood without wasting my 1000 watt power? The 1000 just needs to spread over an area that is 3x3 foot..

I want to be efficient and need all the advice I can take, except - selling my 1000 for a 600 - that would not be very efficient I do not believe in my opinion.

thanks

i dont have any experience with a 1000 watt light for growing but take a look at this.

As close as possible without burning the plants. Too much heat move the lights up. If you can keep the temps down, drop the light. KISS, keep it stupid simple, not really any golden height. All strains react differently.