I arrive at my food requirements using a different method, but I end up at around 22 ounces of food PPPPD for a warm weather 5 day trek.
Ever since I took up weight lifting in college, I've learned to gauge my bodies caloric requirements in order to maintain, lose, or gain weight given a certain activity level. Based on my general dietary knowledge, I try to hit 3000 Kcals per day while backpacking, which should result in a minimal amount of weight loss for me. I'm 5'11" and 180 pounds.
Up until a few years ago, I was not a lightweight backpacker. I carried foods that seemed to work ok for being in the woods for 5 days, but paid no attention to how much weight I was carrying in food. Since moving toward a lighter pack weight, I realized I needed to look at the weight of food I was carrying. And since my total Kcals were pretty much already dialed in, I needed to look at how calorie-dense my food was. This process has caused me to move away from foods such as tuna pouches, apple sauce, and beef jerkey which provide less than 100 Kcals per ounce. I now pack more calorie-dense foods such as nuts, potato chips, ramen noodles, cheese, and certain high fat dehydrated meals. I aim for an average of 140 Kcals/ounce of food.
I will admit, it seems that my backcountry foods have become less healthy, but for 2-5 days at a time, I'm more concerned about calories than the food pyramid. I usually take 2 multi-vitamin tablets per day while backpacking.
So in summary, yes I take approximately 1.4 PPPPD of food the same as you. But I think you need at least a basic knowledge of calorie-density to make this work. I'm sure without even factoring it into your calculations, your backpacking experiences have lead you to an understanding of what foods provide the greatest energy for the least weight. So the 1.4 PPPPD works.