Hmm the original article will be a deep dive into the archives.
Anyway - to catch everyone up - there are several problems with steel drum tire tests, and there are mismatches between drum results and rolling-wheel results, dependent on tire pressure. In the original BQ test, Heine surmised that one primary difference was suspension losses -jiggling- in the bike and rider. Basically any tire that made your body jiggle more was actually costing you energy - and tires that had very low rolling resistance on the drum but that felt harsh had hidden energy costs.
Here is Heine's summary of his views at that time.
Right, sure, but how do we quantify those jiggling losses? That is a rather big task, and the Velus project I linked to above attempted to break off chunks and deal with them piecemeal. Thus:
https://www.sciencedirect.com/science/article/pii/S1877705815014538 <- measuring vibrations imparted to hands
http://journals.sagepub.com/doi/abs/10.1177/1077546315577312 <- how much do YOU the rider actually influence the vibration?
Now, all this sounds like old beardie with SPD sandals territory - I mean
serious athletes don't really worry about body jiggle and want to go as fast as they can on really fast tires. Narrow tires feel fast and should be slinkier in the air and spin up fast. Right? Right?
One person who
really helped changed that perception is Josh Poertner of Zipp/Silca fame.
http://nyvelocity.com/articles/interviews/josh-poertner/
"I was shocked in the early days of our attempt to be the first carbon wheel to finish Roubaix to find that the difference between a longer wheelbase cobble specific race bike with curvy seat stays and numerous ‘comfort features’ and its standard race bike cousin which everybody ‘knows’ is too stiff for riding the cobbles, equates to an air pressure difference of less than 10psi, and generally depending on which bikes you are comparing, the difference might only be 3-4psi equivalent pressure difference between the two."
Pay attention to the section about stacking springs just behind that section, it will become important later.
In the meantime, drum testing has been very scrutinized indeed:
https://janheine.wordpress.com/2018/05/02/testing-tires-isnt-easy/
Now, as to width speed spot. Yes, there is one. And Poertner shows us approximately where it sits:
http://trstriathlon.com/talking-tires-with-joshua-poertner/
Look specifically at the third graph on that page. That is the pressure sweet spot - but it is also the width sweet spot for your body size! (70 psi rough pavement sweet spot in
@Ron 's suggested 32mm tire width is equivalent air quantity to 110 psi in 25 mm. Real Clydes who ride over 100psi in 28mm should look at 35mm tires and so on...)
Now back to that stacking springs idea. Remember how Poertner was talking about running tires with low enough pressure until just short of actually breaking the rim? Now it seems that, if we mull about what we know already, we are eventually going to come up with a
system wheel - wheels specifically designed to work with specific tires. There really seems to be nothing else to do there, and the only way we can change the steepness of the lines in the third graph (which would be the only way to shift the sweet spot) is to integrate the wheel and tire.
Aha, not so fast sir! What if we change the spring rate and lossiness of the air in the tire itself? Well we can't really do
that but we can certainly experiment with stacking different spring rates that are 'tweeners' between tire and rim - enter the tire liner concept. No, not your granddad's puncture guard liners, but foam flex managing ones:
https://www.vittoria.com/us/air-liner-vittoria
(it will come to road too, don't worry)
If, after reading all that, you get the idea that we still don't really know much and there is lots more to come, I agree. Isn't it
exciting? 
