Energy Usage

Why is energy usage now so wasteful and inconsistent—sometimes 8 per image, sometimes 10 per image, and it can even go up to 20 per image? Back then, it was only 6 energy per image, and that 6 energy per image was constant; it didn’t fluctuate like it does now, where it can start at 8 per image and jump to 10 per image within the same timeframe. Is this a bug, or is the new system designed this way?