Of course not, but it does help IMO. But in your case, you riding in ECO and returning with 50% battery, and your wife riding in TOUR & returning with 40% battery, sounds about right to me. Thats because new update EMTB Lite (Tour) powers varies from 120% to 240% output, while ECO just gives 60% output. Technically she's using more power, though you're moving at the same speed. Those numbers can vary even more depending on how efficient the bike is being ridden. There needs to be a balance between pedaling, gear ratio and power mode. From my experience, I estimate 10% power lost while off-roading, especially if there's a lot of hill climbs that day. It might be worth experimenting on your next ride together, is to ride in the same power mode and see what the results.