Cover image on mobile: Down arrow too low on page, resizes when sliding down+up

Hello, I’ve set a cover image with the recommended size of 1980×1485 pixels and well, it’s looking fine on PC as well on tablet or mobile screens.

However I’ve noticed 2 problems on mobile screens, where the second only happens with 1 (Chrome) of 3 mobile browsers I’ve tested.

1. The down arrow is placed a little too low on the screen. After the page is loaded, while the URL bar still is on the screen, the down arrow is just outside of the visible screen. If I slide the screen just enough to hide the URL bar, the down arrow will be visible.

But I think it definitely should be visible once the page is loaded, to animate the user to slide down in first place.

2. On Chrome 89.0 (Android) but not with 2 other Android browsers, I always see the cover image suddenly resizing by a few percent, which looks awkward.
I happens if I open the website in a new tab, slide down a third or half of the page and then let go: The cover image suddenly is bigger. It will resize to its normal size when I scroll back up.

How can we adjust the placement of the arrow, and fix the sudden image resizing?

The page I need help with: [log in to see the link]