FUnny you ask this, I noticed that for my mostly freeway, short trip driving, I got better mileage with regen completely off. Someone explained it then, but it has to do with how long regen is engaged and at force, vs the energy it takes to engage in the first place. For example, it takes "X" energy to engage regen, but if it only regens for a few seconds, it regenerates less than the "X" it took to engage it.
I don't think that's quite right. There's no "engaging" in using regen, no moving pieces or anything like that, it's mechanically very simple. I think the case where no-regen can be more efficient than regen is in comparison to
not braking, rather than in comparison to friction brakes. Regen
should be more efficient in city driving, because you're comparing against a whole lot of flat out waste with friction brakes at intersections.
Imagine you're driving through some nice hills. You go down, then you have to go back up. With regen/OPD, unless you're thinking about it, you'll maintain basically the same speed the whole way. On the downhill, regen gives you a little bit of energy back. Great! But nothing is perfectly efficient, so it's not even close to
all the free energy granted to you by gravity. Then you immediately have to use more energy than you just regained to get up the next hill. If you didn't have OPD, what would you likely have done, if you're not one of those drivers who is terrified of hills? You would coast down, accelerating thanks to Earth's trusty old 9.8m/s^2, then use your momentum to help get you up the next hill. Much less net loss there.
You could get the same effect by modulating your foot on the pedal with OPD, striving to keep the Charge/Power dial as close to 0 as possible the whole time. It's just a pain in the butt. It'd be lovely if Lucid's cruise control/drive assist were terrain-aware enough to modulate that for you, but I'm not sure anyone has done that yet.
