There's a pretty simple solution in 7.1
Add to Home > Design > Custom CSS
@media screen and (max-width:640px) {
section[data-section-id="find your section ID below"]{
min-height: 50vh !important;
}
}
Find your section ID here.
Then adjust the height of your banner by changing the "vh" value.
Note that while making your banner higher, your image will be automatically zoomed in to fit the size of the container.