It slipped my mind that we do have a preference for changing the font size within the app. There are many options under the Preferences such as a Night Mode, Font Size, changing the color of the checked items as well as different layouts. These options are available on the Standard Plan or the Pro Plan.
There is a Preview Pro feature to see the advanced capabilities. The Standard Plan has most of those features minus the voice and a few other things. The link http://www.miracheck.com/plans.html compares the plans.
Also, if you listen to Mira, you don’t even have to read the text
If you don’t want to pay for any plans, if you go into Settings->Display on the iPad or iPhone, there is a Text Size slider that changes it for all apps which some people find useful on the Mini or the iPhone.