As best we understand it there is still a hidden reserve at each end of the meter. Reasons for why those last 4 bars remain are a mystery. My guess is that if you were to floor it up a steep sustained hill you could get at those last 4 bars, or at least a few of them. It may be a reserve for emergency accelleration. Sort of a visible reserve above the hidden one.

When you are coming up the hill, and get to the last 4 bars, try flooring it briefly and see if the assist comes on, it would be an interesting experiment. Other people here have reported getting below 4 bars, but rarely.

This is only opinion, but I don't want to be a fearmonger about pack swings either. I think fears of battery dying are overstated, even if you have large daily pack swings like I used to. And the warranty is excellent so we are taken care of nicely anyway.