Nice! 5.3 is pretty close to your Echo numbers.
The changes you see on the instant gauge will be an engine load-based calculation (measuring either fuel consumption directly, or air consumption and then extrapolating fuel consumpsion), not just pedal position.
But you've just discovered how very tiny changes in engine load (through pedal position) affect fuel consumption, and why basjoos installed a hand lever in his car to gain super accurate control over his gas pedal while cruising. (See his
Aerocivic thread.)
Welcome to the forum!