I have used those type reflective panels in the past; on my Caribou luggage that was mounted on my prior owned DL650. I used the black reflective panels; that emitted a white refection at night when light was reflected from it.
While they are not reflective in the way that SOLAS reflective tape is; those panels will stand out at night and help give you 'presence" in the dark.
The F6B simply does not have enough lighting and reflectivity in the back. This is why I am installing two 16 LED Hyper-Lites. The silver colored F6B is also a good candidate for those reflective panels on the rear. There is ample rear area to install reflective tape; using the black reflective ones would not denigrate the aesthetic looks on the rear of the bike IMHO.
Here's a video I found about installing the same type: