If you think you can eat way over your expended calories using fat instead of carbs you should volunteer for a metabolic ward study where they carefully monitor your calories themselves and activity. You would be the very first person ever to prove this under controlled scientific conditions.
I'll volunteer. You definitely can eat past your maintenance level via counting calories and not gain weight if you go very low carb.
Just because you ingest something doesn't mean you metabolize it. A calorie (Kilocalorie) is a thermodynamic measurement, not a mass measurement. That's the problem with this "a calorie is a calorie" belief. To measure the calorie content of food you use a "bomb calorimeter" to measure the heat content. I used them often in organic chemistry to determine properties of compounds we synthesized.
How a food is metabolized determines the true metabolic calorie value. Put a piece of cellulose based paper in a bomb calorimeter and it will definitely release thermal energy. But the nutritional calorie content of cellulose is zero. Why? Because human digestive enzymes can't break it down.