Just installed a s33 from ac infinity in my 3x3 it says 30cm from flower canopy in the instructions. 

Haven't checked it with a meter and it might be a cm or so high but plants seem happy

I will check it at some point, and fuss over it but I think it's in the ballpark, I'll see how the plants look tomorrow after a daily dose of photons from this fixture.

If they look happy, I will only change it as they stretch and keep it there. 

On the other hand if they look stressed or otherwise unhappy, I will move the light up just a bit let it go again and so on. Nothings exact just really close. At this point too I will start to check things on my app to see if the fixture matches up with the ppfd map they have for the fixture at various heights. 

This fixture runs at 240w  2.7 umol/j which is a good efficiency for a fixture of this wattage. Lumatek are good fixtures too. Your fixture is listed to draw 205W and is 2.5 umol/j efficiency.  Good deal. 

When comparing Apples these are the numbers wattage and efficiency. Reputation too. Someone had to use them first right? 🤔