I've had a similar experience, though not as much variety in my EVs. My lifetime is 4.0 driving how I like for almost 28k miles. I am not a speed demon, but I am not a slow driver either. There are so many factors that affect range. I regularly get 5.4, and can get closer to 6 when driving my kids the 20 miles to school every day (just driving up the 17 and 85, for local folks) with or without traffic. But the way home brings me down to 4.1 - 4.3, depending on how fast I drive. Much of the return loss is just from the on-ramp from 101 to 85 which brings me down to the 4s immediately, especially if I go up it at speed. If I drive too close to other cars and am constantly slowing down and speeding up, I get much lower effeciency than simply leaving space and judging speeds ahead so I don't have to alter my speed as much. Little habits can make a big difference.