I have just looked through the files you pointed out and this has helped a great deal. I was almost thinking that I had misunderstood the gantry 5 framework altogether.
It appears that Home Particles has a specific scss rule for the nav menu forcing transparency and pulling the header (and therefore its background image when containing the Owl Carousel) up to sit behind the navigation for non mobile displays.
Thank you for the pointers. BTW I have now purchased the 1 year dev package! Great support
- This reply was modified 4 years, 2 months ago by dml311071.