Image size (and settings) for full screen slider

What’s the best size for the images which I’m uploading for the full screen slider?
I want my images to look fullscreen on every monitor, indepent which size the monitor/screen is. Is that possible?

And is the full screen slider responsive? When I look at my mobile, the image isn’t scaling in a good way.

I’ve uploaded images with size 1670 x 800 px & at the full screen slider I’ve chosen for “no scaling”.
Should I change something?