Cam is set to record in 1920x1080

When on-screen 16:9 Guide is called, it shows a smaller area than what the monitor is displaying.

However, cam records all that is shown on monitor - NOT only what's inside the 16:9 guide.

I figure that the guide is simply an "action safe area" set at 10% - is that correct?

Correct. The guides are strictly overlays and do not effect the image data being recorded. All image data displayed on the screen, no matter which guide mode, is recorded.

Thanks Ari, love SI-2K camera - fantastic images!

The whole ergonomics appeals to me tremendously.