Header Slider Image isn't so great on multiple resolutions

So, I’m using the Sydney theme, and it’s pretty great so far.

Though, I’m having a rather annoying issue with the main “Header Slider” image on the front page. I’m using a static image, no slideshow, and at 1080p resolution and above it looks great with the menu at the top.

However, on lower resolutions (PC only, mobile/tablet are fine) the black text of the top menu cross into dark sections of the image, and it looks bad.

To test this, you can open the site, window your browser, and just kinda drag around the ratio of the window and you’ll eventually see.

I’ve played around with some CSS to try to get the ratio of all of the involved elements (Menu/image position/location) to stay the same, but to no avail.

Here’s the site.
sparkstestenviroment.website.

Any ideas on how to overcome this?
It can be CSS or any other creative idea, I’m up for anything at this point.

(Site is still a work in progress!)