Whitespace viewport dependency (should CTAs be visible or not)

We've read few Q&A on this topic, also done the research but most of the articles says what whitespace is, not how to calculate it.

When designing for smaller screens, should the whitespace shrink accordingly so all the CTAs stay always visible in the viewport or should there be an element which gives the user purpose for scrolling and then finding the CTA?

Checked few whitespace examples, like:

Apple, Emark.com, Kissmetrics.com/product, Amazon.com Etsy.com

and they all seem to not care about it.