To display a hero image (or video) you need to :

• define the dimensions of TwicImg (or TwicVideo) especially it's height.
• useratio="none"to free aspect ratio
• specify the dimensions of the original image in  intrinsicproperty as inintrinsic="3840x2160"

Your hero media should resize itself according to the viewport while preserving its intrinsic ratio aspect.

Change the dimensions of your browser to see the image adapt it's new viewport.