Shot coverage impact does not make contests stronger, defensive strength sliders control that. Whether the impact slider is at 0 or 100, a 18% contest will be an 18% contest. Now if you lower the defensive strength (release) slider, you can make that same space by the defender be an "open" shot. The coverage impact slider helps balance out real fg % imo so that you can't just pull whatever and have a good chance at making the shot with a decent shooter. More up and down performances rather than most games coming out to 4 of 9 from 3 for that given shooter.
But as another poster said before there is absolutely More than 1 way to skin a cat.