This is essentially it. I think the biggest question mark is the actual temp of the fuel and fuel lines. If they're being measured with IR pyrometer (ie Flir camera, or hand-held optical pyrometer) - those measurements are only accurate for materials who's emissivity matches the settings of the camera. Good ones can be adjusted, but I believe the default values are generally set for reading temps from a theoretical black body (emissivity = 1.0), or very close to a true black body (emissivity = 0.95). The emissivity of a shiny metal fuel line is not a good representation of a black body (emmisivity is much less than 1.0) so the indicated temps of the fuel line are likely being under reported if using IR pyrometer. How much, I can't say - it's probably still ball park accurate, but we should be aware of the limitations.
I also suspect that the amount of fuel line exposed by the m18 cover is negligible regarding addition heat transfer to the fuel in the lines over a different valve cover design. By this, I mean I doubt enough heat could be transferred here via convection or radiation to have a meaningful impact on fuel temp rise across this short section of line. The emissivity of the lines is low (shiny metal) so they won't absorb much radiant heat, they have no fins on either side, so they'll be a poor heat exchanger for convection. And the overall exposed length is relatively short.
Playing devil's advocate, if we assume convective heat transfer on this section of fuel line IS significant, what is the ambient temp of the air under the hood interacting with this line which now acts as a heat exchanger? Heat flows from high temp to low temp. If the air temp is higher than the fuel temp at the beginning of this line, then additional airflow around the line will increase the convective coefficient of the line (which is now a heat exchanger) and therefore transfer more heat to the fuel than if there wasn't air flow around the lines. So if we assume convective heat transfer here IS significant (I suspect it isn't), then the valve cover offering more air flow over the lines could actually heat the fuel in the lines more, depending on the under-hood air temps relative to fuel temps at the beginning of the exposed section of line.
Ducted air will never heat up fuel lines as it will never reach 320k even in extreme situations it might only reach 325k, this is much lower than the fuel lines when stationary as even mine will reach 350k or more and won't drop till the car is moving or ducted airflow is present like I did with a dyno fan to measure the drop.
This is why we also cut the HVAC tray to extract as much heat and as fast as possible at speed which helps with high flow and speed of ambient air over the top of the motor when the hood is closed, thus hindering under bonnet aero. LOL what a joke that thread was.
Good airflow over the top of the motor is essential when running an alloy cover with good circulation and then we get to the rest of the issues.
The first step is to insulate the fuel rail from the head as that is the biggest fuel temp drop, then going one step further and doing a special heat dissipation coating that extracts heat out and reflects any radiating heat from entering it.
Also I powder coated the rocker cover to prevent heat transfer to coils, injectors and wiring that sits in the valley of the head, i could have done
the heat dissipation coating too but it doesn't come in any other color than black and is easily scratched so a decent ceramic coating will do the job to a point but no where near as good but it helps.
I went one step further and ducted ambient air over the top of the motor to help cool the fuel rail, lines and injectors to extract as much of the heat as you possibly can and haven't seen temps go any higher than 325k on the dyno at full throttle in a heat soaked engine bay.
Before it use to hit into late 300 and early 400's without all the work, I can tell you ducting air over the fuel lines has seen a significant drop.
Thats why I never made a cover to hide all wiring and coils as it traps heat, hot coils are bad for spark, hot injectors are bad in lots of ways like spray pattern, cylinder cooling and shortened lifespan, to what extent, I don't know but I was not going to spend any more money but it stopped timing pull and misfires so it did what I wanted to achieve.
If one want's to run hidden lines and covers on their rocker covers and run super heated fuel be my guest, this is how far one has to go
in extreme conditions to protect the n54 from failure which most of you will never experience.
You don't need a science degree to work this out but common sense and a bit of ingenuity which most lack and try to discredit in the name of fanboyism for all the work being done and shared to help others, but go for it and hide your heads in the sand.