Collection product image size options
Broadcast allows you to customize the aspect ratio of your images on collection product grids. The standard setting is 1.0:1 which works well square shaped images. Shopify recommends square images for displaying products.
If you would like your collection grid to show taller images, you can adjust the setting to 1.5:1 and have a longer portrait style display:
For wider and shorter display, adjust to 0.5:1 which works well for horizontal images:
The Product gird options are found under Theme Settings -> Product grid: