Best AFC settings for the GH4 while shooting video selfies?

Hi everybody, I'm hoping you can help me.

I bought the Lumix GH4 thinking it was my dream camera, but I cannot get the autofocus to work the way I need it to.

I run a popular vlog about poi spinning. It's like a kind of juggling. I shoot how-to videos all over the world. People love the travelog aspect.

I mostly shoot selfies. I compose the shot, set the camera rolling, and walk into the shot.

I've been using the Lumix FZ200 for a while. Great camera. But the zoom lens and aperture mean a very wide depth of field, resulting in busy shots.

My dream was to have a camera with a prime lens, so I could let the camera focus on the beautiful background... and when I walk into the shot, it would re-focus on me!

...but I cannot get the GH4 to do this. I'm beginning to think there is actually something wrong with my camera.

Even with face-detection on, it will put the box around my face, but it usually doesn't re-focus. I am set to AFC. I am on burst mode.

I've played with all kinds of settings. If I set single point metering, the camera will focus on me if I stand in the centre of the shot (and close to the camera, taking up 70% of the frame) but if I move around the camera goes back to the background. I cannot find a setting where the camera will stay focused on me.

I had imagined the face-detect would work. The strange thing is that it will detect my face, put a box around it, etc., but it won't focus on my face... !?

Am I missing something? Is my camera broken?

-Nick