The answer to the wattage issue is canopy depth. More watts mean that you have to move the plants away, but you get more space back at the bottom of the canopy.
I use an easy rule of thumb. The top of the canopy can only handle 1000-1200 umols, and you need 500 at the bottom. And with widely dispersed LEDs, you lose about 1/2 of your intensity at twice the distance. It's been measured and it's pretty consistent. So, as the math turns out ... if you need 14" of headroom to get under 1200 umols ... that gives you another 14" until it fades to 500. Your headroom roughly equals your canopy depth. More wattage gives you a deeper effective canopy. If you have 1000 umols at 2 feet of headroom, you'll have 2 feet of canopy.
Your canopy depth = your headroom.
Of course, you also have to be able to run with more headroom to get the deeper canopy - taller ceiling or shorter plants.