Choose the right text feature
Amazon places Text Banner under Accessibility and describes custom font, colour, banner size and timing options. Its current help also provides a tutorial. Begin by moving focus between ordinary menu items and checking whether the banner presents the text you need.
If the problem is understanding spoken dialogue, look for a suitable caption or subtitle track instead. Enlarging a title banner will not create missing translated captions. Keeping these two tasks separate makes it easier to choose a helpful setting without covering more picture area than necessary.
Adjust for the actual viewing position
Use the television at the normal seating distance and compare a few menu screens with different backgrounds. Let the viewer choose the combination they can read comfortably. Record the original settings before changing size, colour or timing so an unsuccessful trial can be reversed.
A useful illustrative comparison is one short title and one longer description. Check whether the longer text remains available long enough to read, and whether the banner blocks a control needed to continue. Do not judge the entire configuration from a single brief label.