Unfortunately, to get the benefit of the slip steam, you gotta be pretty close to the back of the truck. If you have space for good reaction time, you’re probably too far back
This is correct, especially at lower speeds. Greater fuel efficiency would come from lower wind and drivetrain resistance and use of a more efficient range of the motor’s powerband.
Most vehicles are geared for optimal speed to fuel consumption around 55-65 mph (90-100 kph) not 70+ mph (110+ kph). So just going a bit under the speed limit can have a significant impact on fuel consumption.
Also, truckers drive efficiently, so just following what they do will save gas.
But yeah, I don’t go over 65mph and I end up with 7-10mpg over my highway rating.