Hero Image Issues on Theme

Site is currently being worked on here

First – the hero image specs are not correct at all. I have tried a lot of different sizes and none seem to fit well. I don’t think is an issue with image I’m uploading. I love this theme but the sizing on different screens makes that background image wonky. If you look at the site then change your browser size you can clearly see the image get distorted different ways (mobile especially looks bad even though some of the page is responsive and stacks).

I don’t know what the secret is to fix this but I can’t use the theme unless this works well – anyone have ideas?