AIUI, the ideal contact with the road for minimum drag (also minimum grip) is a circular patch. Narrow tyres tend to give an oval patch, along the road, fat tyres tend to give an oval patch, across the road. The 'sweet spot' (for drag) is therefore the width that gives you a circular contact area, for your weight and preferred pressures.
Casual observation shows that even wide tyres have lengthwise contact patches. Longer contact patches may deliver more security by bridging across small slippery patches of roughly circular shape, such as oil drops, stones, or even wet leaves, but otherwise why would that contact-patch shape afford better traction?
The main source of rolling resistance in tyres is energy loss to hysteresis: the tyre returns less energy to the bicycle at the back of the contact patch than it took from the bicycle at the front of the contact patch, due to damping in the tread and casing. Wider tyres have less total flexure of the casing and tread, thus lower damping and rolling resistance. So rolling resistance keeps on decreasing as you increase tyre width, subject to the pressure being the same. I am aware of no “sweet spot”.
In practice, of course the pressure should not and anyway cannot be the same as the tyre gets wider, leaving lower suspension losses in the rider as the main reason wider tyres may roll more easily. (In some cases there’s a strict rolling-resistance benefit to wider tyres even at the lower pressures needed to leave casing tension unchanged, but you’d need lots of highlighter pens to show why.) If there is a practical sweet spot, it’s where the tyre width and model allow you to use up all of the tyre’s casing strength in the hoop-tension orientation at the pressure you prefer, thus proving that the casing is not needlessly strong (i.e. lossy) for your particular use. For light riders (like me) that’s usually impossible: the casings are always too strong. Put another way, heavier riders often enjoy a lower Crr.
The whole concept of a scaling factor for suspension losses is wrong, because suspension losses increase with increasing pressure whilst casing losses (rolling resistance as measured on a drum) decrease with increasing pressure.
It’s not obvious to me why the second part of your sentence follows from the first. Would you explain? Anhalt just multiplied the rolling resistance from drum testing by 1.5 to account for the approximate additional losses in the rider from road vibration. He isn’t claiming the factor always applies, and clearly it cannot. It will be higher on a rougher road, with a lossier rider, with a tyre at higher pressure, etc., etc. But if you’re going to make a chart of rolling resistance versus drag to attempt to find the best tyre width, you need to make some assumptions. This seems a reasonable one, no?
Joshua Poertner’s work is interesting too. He and Jan Heine have been a good tag team in favour of wider tyres. It’s curious that these fringe characters have popularised a movement that mainly profited the big players like Specialized.
