The surface area of the chip is not large enough to allow lenses to make much difference. The reflector it has is actually more suited for creating better uniformity, as it increases the surface area of the point source. The issue is not really at all to do with power, but to do with the concentration of energy in a narrow region. Which forces the grower to raise the fixture, in order to equilize the hotspots. Doing so however increases the radiative and reflective losses by quite a large amount. By my calculations, going from 12" to 36" is a loss of roughly 25%. Though with reflective walls you can gain about 10% back, maybe. The overall photon flux is actually not powerful enough to support areas larger than 4 x 4, however these are designed to be used in daisy chain with other fixtures, to equalize the flux and uniformity deficits that a single fixture has.
The options available here are really quite small.
#1 Use a larger grow area to suit the fixture. (Not ideal)
#2 Or reduce the power of the fixture to suit the grow area.
#3 Or if possible, hang the fixture at the appropriate height and accept the losses.
After closer inspection, there possibly looks like current and voltage modulators on the meanwell driver. So could be something to look into, or perhaps through external dimming equipment. However, using dimming will ultimately lower the potential yield, so much in fact that it would probably be better to just use HPS. Im sorry if this is not what you want to hear. But the design of the light makes it difficult to implement for small grow areas, to the point that it ends up being not any better than what you are probably trying to replace (HPS).