Penetration treatment is an evolving science and as such there is still a good deal of confusion regarding best practice standards. That said, changing standards takes time and it should particularly when safety is involved.
The 3” clearance standard is one of the evolving areas that needs better clarification; however the intent has been, and still is, to safely managing light bulb generated heat.
When first introduced decades ago fixtures used incandescent bulbs that have 4000F filament heat. Even a 60 watt incandescent bulb can reach 500 degrees F and wattage in use then was as high as 150 watt.
Allowing that extreme heat to escape was critically important, however the exact science of how the 3” space was reached is somewhat unclear; but again the clear intent was to prevent dangerous heat entrapment.
Even then the requirement for 3” clearance from the wiring compartment was debatable. Tests show that the housing functions as a heat sink for the heat source centered within and the air separation between the housing and the wiring compartment does not directly conduct but rather is subjected only to diffused radiant energy within the air space. Ironically that basic physics and need to separate the junction box from the heat sink to keep the compartment from overheating was well understood by the engineers that designed the fixtures.
With the introduction of insulation contact rated fixtures this 3” requirement was obviously eliminated even though the fixtures were identical except for lower wattage light bulb use.
We now know that insulation contact with the fixture causes many unintended problems beyond light bulb heat and that fixtures must be effectively isolated from the attic space and incorporated into conditioned air space.
That means that clearance understanding is evolving to better address actual heat transfer and diffusion within the system.
CanCoverIt™’s square/rectangular shape makes it easy to install but more importantly the shape is critical to optimize diffusion air space volume within space confinements. (Conversely a round shape provides about 21% less air volume around the fixture and therefore less effective heat diffusion space.) Again the more specific objective for clearance specs is to safely manage light bulb heat.
Heat management regarding newer fixtures is already aided by the fact that the light bulb generated heat is lower and therefore the 3” clearance from the heat source is very effective for allowing the heat sink function of the fixture. Because the compartment is separated from the heat source and is only subjected to indirect diffused radiant heat it therefore doesn’t pose the same heat danger and heat mitigation requirements.