I've never heard that calculation, but I think I'll use it in the future! It is definitely the right number of calories for me when hiking (or sitting, ha,ha). I hiked the AT and started in shape, always being hungry. I became more and more uncomfortably hungry and at different pts. in the hike had trouble with carrying the weight of the food vs. being hungry. I ended up carrying more weight than recommended, but did better.
I would recommend even if you're not hungry and are looking to lose weight, you make sure you're eating the minimum base recommended for you to ensure you don't lose energy. I think once hiker hunger sets in, most people are already hurting for calories!
I also like your idea of carrying PB. I was laughed at for carrying the weight of a jar in the beginning of my hike, but it was a great way to supplement calories when needed and I think worth the weight. (mashed potato powder helps too and is light!) I don't think powdered PB has the fats that jarred does and I don't think I got enough fat on the hike which maybe impacted my joints and led to a really low body fat %.