Totally agree! I have done some researches on CTA and figured out the role of whitespace in Web Design. Also, I carried out A/B test and get the higher rate of click with the design using more whitespace. Obviously, when place a CTA button among whitespace, you concentrate people on your CTA. It is the effect of contrast in Art. Very useful!
Check out my CTA design, I hope it will be an example of how to apply this rule in web design.