I was able to get it to the top bar. Don't ask me how or what I did, other than keep the car moving more from the engine, coasting or braking. It didn't stay there too long, so I don't know it it really matters much. Also, I've been on the opposite end where I've exhausted the battery with all the stop and go traffic and the engine kicks in to charge the battery.
I picked mine up about a little over a week ago and they said it would never show completely full (usually be two bars below the top) nor would it ever show completely empty about 1 bar below the bottom.
Don't worry about the last bar. You will rarely if ever see it fill up and your dealer should have told you that. If you are going to try to fool around in EV mode you want the battery as high as possible as it won't engage at a low charge. My foot just isn't light enough to keep it there for very long.
Toyota 'and' Lexus have designed the system to not over charge or under charge. By design you shouldn't 'regularly' see the battery bar at the top mark to keep it from harming the battery. Nor will it discharge to the bottom bar for the same reason. Like others, I saw it at the top once, but it was coming off a mountain. I think the braking went to full hydraulic to draw battery power (electric braking system) but it was the only time I saw it and it was quite some time ago. At that point I'm sure the re-gen system turned off.