Hi, I'm having the same issue with my portfolio site.
I can't figure out what the CSS would be on my template to force the main image on my homepage to resize for mobile screens. A bit off topic, but I'm also curious how to change the visibility to none on my site title on just the homepage as well.
sacha-marie.com
Any help would be appreciated! Although, the mobile resizing should really be a toggled feature built into all official Squarespace templates...