Full Width Slider Size Question

Hi,

What is the correct size for an image on the full-width slider that covers the screen under the header across all browsers? So far, I have experimented with different sizes and none of them work correctly. I could save hours of time if you actually published this!

For example, on Firefox it works perfectly, on Chrome and IE it leaves a gap below into the next content. It’s a little frustrating. I have added below.