Hiri has two different layouts to view your emails, based on the information density: Low-density mode and High-density mode.
High-density mode (default)
This mode lets you see many mails on each page, but gives you less context with each mail. You can see the sender, subject and dates in this mode.
In this mode more context is shown for each mail, but fewer mails are displayed on each page. You can see the content excerpt from each email and this helps you deal with mails more quickly because you don't have to open each email.
To change the layout, go to Settings -> Appearance and select one of the two modes. The listing of emails will instantly switch to the new layout.