Sorry for our late response.
First of all we would like to ask some questions to fully understand this issue.
When disabling sticky mobile header does it solves this issue or that doesn’t suite you as a solution? Also did you modify other header CSS values except padding?
Hi! Turning sticky header off didn’t solve the mobile view issue (also we’d like to use sticky header). We haven’t used any custom css on this site. We only tried adding custom mobile padding in the first section of the front page. In order to prevent the first heading from being hidden under the header in landscape view, we would have to add so much padding that it would not look good in normal mobile view.