My apologies for the delay.
You can use some custom CSS and a mobile media quiery to adjust the height and width of the welcome section on mobile devices. Currently it set to be 100% of the window height on mobile devices, but you can set it to be 100% width and auto adjust the height.
If you go in the style.css file of the theme, at the bottom, there is a section for mobile device specific CSS code.
The “trim” at the top is aprox 70px.
Also, you will want to reduce the welcome image in size, it is very large and takes a few seconds to load. You can reduce it down to 1920px wide which will work with most screen sizes.
Hope that answers your questions.