When you fill up your tank, how much range do you get?
I found that at 65mph on the highway it's better to keep the ice running and the HVB full than let it drain and recharge all the time.
I never draft trucks, I don't feel safe I can't see the road ahead so my numbers will be lower than yours.
I get 700+ mi. local driving and 500-650 mi. on the HWY on a full tank. Here's my Fuelly.com Link: http://www.fuelly.co.../ptjones/163299
I tried your method a couple of years ago, but it didn't work as well as 2 Bar accelerate to 5 mph over and EV to 5 to 10mph under and repeat. This is like P&G and the Science behind it is the ICE is most efficient at 2 Bars but that is to much power for maintaining 65 mph maybe up to a factor of 3 so part of the extra power is use to accelerate and the other for charging the HVB. If you use the ICE all the time the ICE efficiency is way down using maybe 1 1/4 Bars and wasting energy to the radiator.
There is a direct relationship between the lower percentage of ICE use and higher MPG's. The two tanks that I got 68mpg, my ICE % was 28-30%, that is why the 2 Bar rule is so important, when you use less than 2 Bars the ICE runs less efficient and longer so you lose more heat to the radiator.(water pump doesn't run when ICE is off) Running above 2 Bars, the HVB doesn't charge faster and the ICE is less efficient. Obviously it isn't practical to only run at 2 Bars all the time because of driving conditions, but the more you do the better MPG's.
The improvement in FE drafting is dependent on the air speed going by. With a 30 mph tail wind going 70mph you would probably see about 1 mpg improvement, but with a 30 mph head wind going 70 mph = 100 mph so your improvement could be 6 mpg or almost 100 mile improvement of range. BTW I hate getting 32mpg with 30 mph head winds and uphill climbing, what a drag.