Why are the rewards for low difficulty higher than those for high difficulty?

[XiaoWXHang]

difficulty 17: rewards 0.00000000011 ore
difficulty 9: rewards 0.0000000898 ore

[Swazuto]

How long did you mine difficulty 17 and how long did you mine difficulty 9?

[dannpl]

That's not a problem. depends from the time to solve the challenge and send the tx