So rather than guess at the data sheet numbers I decided to pull them up…
I’m pretty sure I located the cob you’re looking at. Do you see where it says the same cob at 1140ma and 25c is 180 lm/watt? Or at 1710ma 161 lm/watt?
Not that you’ll be able to keep them at 25c, but even at 50c you’d only be giving up a few. Double the amount of cobs and cut the current in half and everything will go together a lot better for you. They’ll be much easier to cool, and you’ll have a much better spread of light. The average builder is probably going to recommend 12 cobs minimum for a room your size, their effective footprint isn’t all that big. You can certainly bump the current a little to cheat that, but I don’t personally feel like going that far would be in your best interest. 4 of them at 75 watts each is probably going to create more par than a 400 watt hps, regardless of the amount of lumens produced.
The lowering and raising of light is indeed to change light intensity. You make a somewhat valid point about the reflection, but reflected light isn’t 100% efficient. So raising your light decreases the light intensity everywhere. If you have to raise a light to get the wall, you can also assume the amount of light then getting to the reflective wall will be less, and less than 100% of it will reflect onto your canopy.
This is also partially the reason you don’t see 4x4 light fixtures take up the entire top of a 4x4 tent. Light manufacturers play the reflective wall they assume you will have into their favor. Most of the quality led lights you’ll see a window where the light is raised and center par readings will go down, but edges will come up. Personally I prefer dimming over moving. But dimmable driver and dimming source cost extra, and some people aren’t as lazy lol.