Having said that we saw Luapula at Mahangu, I was asked in a private message from Joakim (Djerf) to post some photos of them.
I wasn't sure about this, since we didn't get good shots from the back, but anyway here are two representative views. My wife and I had a fairly short trip covering a lot of area, so we didn't have time to wait around to get really good shots.
I have included a map of the spot, in case anyone visits. On the day we took these photos, we had great sunset views of a variety of animals at a waterhole, and were on our way back to the lodge. Our guide, young but very experienced and part-way through producing a photo-guide to the birds of Namibia with his father, said that this was a 'Black-backed Cisticola - Luapula' spot, and we stopped to see if we could find any.
We have photos of the back of the bird from that evening. But it was already nearly dark, so although the patterning is clear enough, they are not good photos. Also, my camera was set for the sunset shots we had taken 30 minutes before, and in the minute or two we saw Luapula in the evening I didn't think to reset the ISO even higher. (We got OK binocular views.) And it was 1st January and I was still hungover from the spectacular Mahangu Lodge live music New Year Party the night before, so that didn't help my photography either.
The following early morning, we got some OK shots from the front, one of which I posted earlier, but it wasn't possible to get behind the birds, so no back shots in good light. And we had no time to hang around as we needed to drive to Mushara (Etosha) that day.
By the way, I looked at Luapula in 'Birds of Africa South of the Sahara' and it has what seems to me a much more accurate picture of Luapula than does Sasol. Indeed BoA specifically labels the 'grey tail' which you can also see in my photos, whereas Sasol shows a bright beige tail.
Anyway, sorry about the quality, but I hope someone can get some information from these photos.