The short answer
On the testimonial item, open Content style under Testimonial Content Area. The default is Large (text full-width). Large uses the theme Lead Paragraph size. Small and Blockquote use those theme text styles.
A closer look
Each testimonial has its own Content style, directly under Testimonial Content Area. The choices match other Smithworks content areas: Default, Large (text balanced), Large (text full-width), Small, and Blockquote.
The default is Large (text full-width). Large uses Theme Settings → Typography → Lead Paragraph. Balanced keeps line lengths even. Full-width lets the lines run the width of the column.
