Ok, try this code and add it to the Custom CSS field of the Custom Code section in Integral Options Panel.

@media (max-width: 767px) {
	.navbar-fixed-top {
		position: fixed;

The background images are made to always take up 100% of the height of the section otherwise you would have blank white space. The fact there are long testimonials affects the height of that section, which affects the background image.

Nice site by the way, you’ve done well with the theme.