Well with your board you probably can't because of the IR which is a benefit. Not 100% but I dont believe the timbers have added IR. This would explain why you see what you do but not for the reason you stated of radiant heat. Can you link your exact timber fixture? As I stated there are differences in QBs and some can be run less than 12"s away..
Also as for your lix statement it just so happens lux meters do not pick up IR or UV and poorly pick up red and blie spectrums. So the ppfd (actual light intensity) can vary a lot and is particularly why lux should never be used with blurples. Often you see bleaching and light stress when ppl try to do so. Basically you are giving the plant under the
HLG far more ppfd so you can actually reduce the intensity and adjust the height for even spread. Its not as simple as recommendations.
Its not a cop out. Its that I have done this time and time again and everytime I go into an led thread I have to go through a million things to get ppl to understand what I'm talking about and I'm just as I was years ago burnt on it.
There are reasons you see what you do in your grow but its not for the reasons you are claiming. Its a topic can can be discussed for years and in the end the answer is there is no right answer or one best light.
For instance the addition of IR changes many variables from light distance to changes needed in environment. Side by sides only show how well it works in one set of conditions. This is why they are flawed bit many ppl see them as an end all be all. Both lights should be run in their optimal conditions. With IR you can't run room twmos as high which changes everything from nutrients needs to watering times.
So I'm just gonna drop it if ya don't mind. Rather not spend a year in this thread just to come to the conclusion there is no right answer and there are reasons why some lights do better under certain conditions.
In short your cobs run closer because they are lower wattage without IR added bit also producing less ppfd even though the lux is the same. The same can be done with QBs and even more effectively which is also true can be done with the cobs.