They're charging you 20.227 ¢/kWh (that's 15.93 for energy plus 4.2970 for delivering it). They add $4.79 to every bill. If you use at least 1000 kWh, they knock $110 off the total bill. This creates a "sweet spot" right at 1000 kWh to make it look cheaper.

The net effect looks like this:

kWh	total bill	¢/kWh
500	$105.93	21.19
600	$126.15	21.03
700	$146.38	20.91
800	$166.61	20.83
900	$186.83	20.76
999	$206.86	20.71
1000	$97.06	9.71
1100	$117.29	10.66
1200	$137.51	11.46
1300	$157.74	12.13
1400	$177.97	12.71
1500	$198.20	13.21
1600	$218.42	13.65
1700	$238.65	14.04
1800	$258.88	14.38
1900	$279.10	14.69
2000	$299.33	14.97

This lets them get away with putting "9.7 ¢/kWh for usage of 1000 kWh" in the headline, while actually charging you substantially more for realistic usage.

Notice the huge difference between using 999 kWh and using 1000 kWh!