Thanks, I see it now. Viewport Actions are currently based on the document and not the window; this effectively means they can't be used correctly in iframes. It sounds like using the <div> method for the wordpress plugin will solve a lot of the problems (but may cause others for you based on how your site is made).
There is a newer technology called IntersectionObserver that can be a solution to this problem. We plan to adopt it for Hype's waypoints, but until then you can manually use it. I believe there's a couple examples in the forums with an "IntersectionObserver" search. Just be aware it does require semi-newer browsers to use.