Fixed elements, such as headings, bottom navigations, floating action buttons, etc, should be spaced from the artboard edge depending on their responsive-resize anchors.

Eg. a header will always be anchored to the top, so that when I resize the artboard, it will stay at the top. Therefore it's position in the prototype will be measured from the top of the screen / artboard.

So, what I am trying to say is kinda hard to explain without an example, so I made a video: https://www.youtube.com/watch?v=IjslfRSa1QY

My attempt at a textual explanation below:

A floating action button, however, will be anchored to the bottom right of the artboard, so that when I resize the arboard it will stay in the bottom right corner and maintain its distance to the artboard borders.
Therefore, when marked as a fixed element, its spacing shall be determined by the distance it has from the bottom border and the right border.

Currently fixed elements are not relative to the arboard's entire size, but only to the artboard-viewport size. This leads to them being in the way when designing and obstructing the view. Additionally it is also harder to judge how much space is needed at the bottom of the design in order to accommodate fixed navigational elements.