Now! has 400cal/8 oz cup and Horizon 420cal/cup not a huge difference so possible it could be the bioavalibilty or they really like the taste.
The companies could have the same type of extruder. It is what makes the shape.
Most avg energy dogs need about 400 calories per 20 lbs, differences are seen for energy level, activites ie dog sports, and metabolism of individual.
Most adult maintance dog foods have about 375- 400 cals/ 8oz cup and performance 450-475 cals/cup with a higher fat content. A dog biscuit like a 1 regular size milk bone have 85cal per bone or equal to almost 1/4 cup of food. So think about your treats when you are trying to get your dog to lose weight and minus that amount for the total fed.
My parents Lab was really heavy, 120lbs. They had no idea why. I observed them feeding her large dog bisiuts when she came inside sometimes 3-4 a day. Those treats were around 210 calories a piece. So times that by 4 and that's 840 calories over 2 extra cups of food a day. Doing nothing else but stopping treats their dog lost 40lbs in a year.