Changing the mobile breakpoint view

The mobile breakpoint view in Blocs appears too small for most current mobile phones, which have a high ppi and much higher pixel width. Using the developer responsive views available in Firefox, Safari and Chrome it seems that one can’t expect the actual mobile phone format to correspond to the one seen at the Blocs mobile breakpoint. Can this setting be made customizable? I don’t find a means (which, admittedly, could be right in front of me.) A mobile-first approach makes this essential. Thanks.