Remember the assistance level you use have a massive effect on mileage.
For instance my crossfire / suntour setup has ...
No assist, pedal normally. It's hard on inclines (but that might be my OA) , I find a high cadence helps.
Low assist, this at a given pedalling force will allow you to achieve say 11mph with little effort.
Tour, same effort from you, you will achieve say 15mph, but the drain on the battery is higher, less mileage achieved.
Climb, really gives it a boost on hills but even more drain on the battery, even less miles.
Sport, just gives it full whack, same scenario.
All kinda obvious but what I do to maximise battery life / mileage is constantly switch between no assist when I can (on the flat, downhill or if the wind is behind me) and try not to use anything above low assist most of the rest of the time. So normally, you aim to use a low level of assist, this also helps you maintain some fitness, not getting the bike to do it all for you.
Your level of health /fitness will dictate how much assistance you want. 7 years ago I'd be doing 50 miles on a roadbike hard. Health issues now dictate a 10 to 15 mile assisted ride is all I want or can do , but without it, I simply wouldnt be able to enjoy riding at all, period.
An ebike is a marvelous thing for that, its kept me out there.