Russel,
I'm still running the b27 firmware and the DNG format selection is present in that one, If you haven't already done so, in Settings select camera type as CGO 3 Pro. Turn on the advanced feature mode. Now go to the ST-16 screen and select the video icon, then tap the tool icon and change the video setting to 4k-25fps. Exit the video mode and select the camera icon on the screen, then re-enter the tool mode and scroll down the list for picture type, turn on the histogram, select the desired histogram metering mode and scene setting. It's probably all there but you may have been over looking it. The H alsohas to be turned on to access the camera tools menu.
Whenever you are shooting photos (in photo mode) be certain the video has been set to 4k before taking off, then switch to camera mode. Although you will be using the camera mode the video setting effects the photo resolution and 4k provides the highest resolution. Once set the ST-16 will retain the video setting from flight to flight, the photo type (DNG,JPG, or both), scene selection type, and keep the histogram turned on. It will not carry the histogram metering mode over to the next flight, you'll have to reset it for each flight. If you did not already know the histogram can be dragged to anyplace on the screen.