This is very good question. I made some observations during my last 2000 mile trip with various combinations.
1. As someone mentioned above, speed is the biggest factor in the range. I have gotten range of 350 miles few times and only 270 miles few times. Main difference is speed. If you can keep under 65, you get the best range(330-350),if you are pegging 80+ you will only get (270-280).
2. Air-conditioner has some impact, but not as much as I thought. My guess is it would not make range difference of more than 10 miles.
3. Hills/mountains did cause some range loss, but surprisingly not that much. Lost range recovered while coming down(not fully for obvious reasons).
Now, to answer EAP vs Manual. In real world scenario(not like those tests of running in a controlled loop), you can always get better than EAP. It is not because EAP processing, it is because of its aggressiveness.
These are following I observed, hence stating as aggressive:
1. When a vehicle moves away from your lane, EAP stabs the throttle to reach the set speed( pretty aggressive). This burns more energy.
2. It constantly trying to maintain same set distance, unlike our driving where we smooth out those variations when traffic speeds varies because of traffic and or speed change in that road. (Say speed changes in the road from 35 to 55) .
3. Some wastage of power because of Phantom braking for shadows, overpasses etc.
In my experience, I can always get better range than EAP in real world scenarios. But again if you are driving on a major highways without much traffic, it may not make difference if you drive vs EAP drives.
Keep an Eye on Power used/Recovery bar above speedo (Green vs Black), you will see the difference of how long black bar is when EAP vs your driving. That will tell you who is more efficient.
This black bar is your friend to get the best, for efficient driving. You are driving more efficient if the black bar is smallest, and you are coasting when there is neither Black or Green, and this is where you should strive to get the best. Coast whenever possible.
I wish there is a setting where we can specify the how smooth/aggressive EAP can reach set speed.
Also wish some kind of coast option is there, and when you lift of your foot from accelerator slowly, it recognize you want to coast and does not apply regenerating braking until we touch brake. But if you lift of foot fast from accelerator pedal, then apply regenerative brake.
Yesterday, I drove our minivan after longtime to ferry folks from airport, and I realized how far its coasts, it coasts miles and if there is even slight downward incline, it keeps coasting. Wish we can coast like that when needed to avoid regenerative losses.
Currently, we can get into coast mode by keeping accelerator in correct position relative to speed, but it is bit tricky and needs a constant watch on that bar.
If anyone observe, the accelerator pedal position is directly proportional to speed or speed of Motor since it is single ratio gearbox. (unlike ICE, which proportional to Throttle opening, not RPM).