Yes the space is mostly coming from that .site-inner div that I posted in my previous reply. If you want to reduce it then that’s one of the places you can start.
One of the reasons that space is there is to push the site content down some to prevent it from showing up to high or behind the header. The header area is an in a fixed position that doesn’t move, and when you do that, everything under that header has to have space added to compensate (this happens on any site/theme).
If you want to easily fix this, then I’d disable the Sticky header through CSS…especially if you’re going to have multiple widgets/content under the header. Otherwise it’s going to take some effort to create some custom CSS code to keep the sticky header while also adding in those multiple widgets right under it.
In order to do either of those it’s going to require some CSS.