Could you possibly provide a screenshot of where you're seeing extra white space?
Just took a look on my computer (Mac Pro 5,1) and can't see any white space at the top, either in the designer / editor view or when it is in preview mode. Obviously I can't see the published page but wouldn't think they'd be too different.
Are you perhaps getting the 'white space' when you are scrolling the page?
If so then a lot of browsers do (for some reason - I'm not sure why - hopefully someone else can answer this one?) scroll further up and down and also left and right than the site should allow. Some sort of built in browser scrolling happening there though and not always the site design.
Anyway, if you could provide a screenshot or maybe even a screen-recording which would really help too.