My 2 cents on this bigger tyre impact.
Let's say it's 2percent bigger circumference, over 100 miles reported on the odometer, you would have actually travelled 102 miles. The ECU does not know this. MPG calculations are based on odometer reading, so in theory it shouldn't impact. In practice though, the car would have worked 2 percent harder over the reported 100 miles, so you may see a minor dip in MPG on the display. But since you know you've traveled the extra 2 miles. You can calculate to compensate for this dip. In real life though, there are more MPG impacting factors like traffic, road surface, weather etc, so unless testing on a dyno in a controlled environment, it will be hard to detect.