From version 1.4, the app has a resizable news reader window, where you can drag the sides of news reader window to resize it.

You can also open Preferences / Appearance and then set Article Reader Width + Height.
Category: News, Feedly, Feedbin, RSS
Compatibility: MAC OS X Yosemite, El Capitan
Newsflow: News Reader for Mac OS X (Yosemite, El Capitan)

Newsflow brings news from all of your favourite websites right to your desktop. Enjoy your articles in a fast, fluent and highly customizable news reader.