The numbers don’t mean you will necessarily ‘feel terrible’ rather than not ‘as energetic as on a feeding day’, only the max amount of body fat you can utilize. Being fat adapted on keto for several years means that you are metabolically flexible and change fuel sources seamlessly. The rest of the energy comes from another source: mostly lean mass, but as you note also probably some glycogen. The glycogen is muscle mass dependent specifically, plus a little more in your liver.
Another example: myself. I weigh 145 pounds and have 14-15% body fat - so about 22 pounds. Close to your numbers. I’m a bit older, though, so aren’t into long fasts or your intensity of exercise. But I’m no couch potato. I do what I call an overnight IF 3 or 4 times per week. That’s simply timing the last meal of a day to be about 12 hours prior to the first meal of the next. I feel very little hunger on those mornings. If my mid-day meal on a work day (I work full-time at Walmart) happens not to come until early to mid-afternoon - up 6-7 hours after my morning meal - I still don’t feel very hungry. Just a passing and gentle reminder that it’s time to eat. My energy remains the same regardless.
This is what metabolic flexibility feels like. If you and I were to fast for several days or longer, then we would quickly see first the fat mass and the lean mass disappear and overall energy expenditure drop as our bodies attempted to compensate for the lack of incoming fuel. If you don’t believe me, try a 14 day water fast.