Not sure what you mean by Page Clipping Area Steve
OK, to see what this actually means.
On the page that you have unlocked and moved down by 24 pixels, drag a guide to it's top edge and bottom edge while in normal view.
Now switch to line view.
You can easily see that the page area has in fact not moved at all therefore if you were to have any content in that lower space, it will not show in web preview or when exported because it has been 'clipped' by the page area.

Dragging the rulers intersection to 24 pixels ABOVE your page top has the result you want (the 'air') without the consiquences of page clipping.