I’m trying to input banner images to display behind page header. What size should these images be to display properly? I can’t find documentation, but I’ve tried a few sizes and the theme is stretching and distorting them to appear very blurry. I’ve tried at 1500×300 and 2100×600 and even with large size/width; they are getting stretched and distorted. You can see an example at https://9zl.90f.myftpupload.com/executive-coaching/.