As no-one has responded I dug out my own copy of the 2nd edition of David Johnson's Ingleborough book. A quick glance suggests it doesn't appear to mention the Pot Scar cairn directly. But pages 105 to 157 are devoted to the local archaeology, so by reading through that you might spot clues that help. Mention of comparable structures may guide your thinking on the cairn in question. Your local library would get it in for you of course. Or I think they're still selling copies at the Yorkshire Dales Millennium Trust office in Clapham. Can't remember the cover price but I don't think it was expensive. It's a nice book and perhaps worth having anyway.
I'd like to bet that someone in the Ingleborough Archaeology Group would know the answer. If you're keen to find out you could find their website, make contact and ask?