Hello 77, Led light manufacturers rate their lights in a different way. Mine says it got 300 watts but when you plug it in the wall it only uses 145 at the wall, and the 145watts is what you go by, most manufacturers are like that.
What kind of light is yours ?
Is the 750watts at the wall or is that what the manufacturer says?
If the 750watts are the actual power draw, I would start by hanging it at least 26-32 inches maybe higher depending on how your young plants react .
Hope that helps some,what did your light maker have in their instructions?