With the utmost respect for your experimental explorations, I think you may be trying to achieve what is already being achieved with Torque Sleep without any driver intervention in both D and non-D vehicles.
The alternative would be to just use AP and relax but then I know sometimes you need to take over and so I understand your curiosity but safety, stability & roadholding are way more important than gaining extra kilometres, so personally, I wouldn’t attempt it just like I won’t be drafting again for relatively small gains. In any case, once the planned SC’s are operational, there won’t be a need for any of this.
From memory, my best figures are something like 165 Wh/km @ ~100 km/h but that wasn’t the average for a whole hour. Then there are so many other variables apart from speed: gradient & elevation, wind direction & velocity, total passenger & cargo weight, barometric pressure, external temperature, humidity
?), HVAC settings, tire type & pressure, rolling resistance (as you say), road surface & quality, vehicle model & age, etc. all have an effect to varying degrees…but then I think you already know all of this, being an EE