dan

Hey I was using this for both the genesis responsive slider and soliloquy and even the royal slider on other genesis themes for insync it should work but

note: bosses-pro is a theme I was working on so add your div there of course..

also this is not exact for insync ill report back if I add this to insync I think I will try as I notice now there are 2 slider widget areas one fullwidth assume thins works than disregard this post..
It should fill out the whole area top to side and you should have a height that you can adjust if you want.. the key to this is it is 100% no set width and check your media query if it does not resize correct.

/* Genesis Responsive Slider
——————————————— */

.bosses-pro-home #genesis-responsive-slider {
border: none;
padding: 0;
}
.bosses-pro-home .flexslider .slides img {
width: 100%;
}

.bosses-pro-home .flexslider {
max-width: 100%;
}

for soliloquy I did this below and more because I had captions..but this worked well for the fullwidth effect..
.home-slider .soliloquy-container {
max-width: none !important;
max-height: 100% !important;
}

.home-slider .soliloquy-container .soliloquy-image {
width: 100% !important;
}