Conor, in skin/reboot/css/reboot_sliders_carousels.css
Replace...
Code:
/* preloading images */
.owl-item.loading{
min-height: 150px;
background: url(../images/loading.gif) no-repeat center center
}
With, eg.
Code:
/* preloading images */
.owl-item.loading{
min-height: 296px!important;
background: url(../images/loading.gif) no-repeat center center
}
With 296px being the largest scaled height of the slider images in desktop view.
You can set..
In skin/reboot/js/reboot.js