You may have noticed that when Rich Capture is switched on, it is actually switched to 'AUTO'. This is a new "feature" for the 550, 950 and 950XL.
The phone will automatically decide whether to use Rich Capture based on the composition (it will only switch on if it detects extremes of light and dark, or if you are using the flash).
Unfortunately there is no way to force Rich Capture to stay on like you can on the older handsets.
In my time with the phone I took around 30 photos with Rich Capture set to Auto. Only two of those photos were actually Rich Capture shots with the 'choose the best lighting' option.
I would suggest taking a photo of with extremes of light (such as a half sky, half ground landscape composition).