In my observation of different types of lights, I think that a soft-driven , multiple COB fixture works like a spray-bottle set to "mist" -meaning that the light from multiple, soft-driven COBs will distribute the photons over a larger surface area....but will not penetrate very far into a canopy. Therefore, it is very important to alter the style of growing to accommodate the nature of this type of photon distribution -a la a scrog that spreads out the overall surface area of the
plants to form a shallow canopy that does not require much light-penetration.
With HID, the opposite is true. With HID, you have a photons flying everywhere from the bulb with only a relatively inefficient way to corral them -like a reflector. But, IF you take the best advantage of the nature of the bulb and apply it to a vertical style grow, then those otherwise "wild" photons will not be lost -thus making that style of bulb-use much more efficient.
So...then...which produces the best results between the two styles? I wonder.... I guess if ttstykk's experiment pans out, then we shall see!