Documentation:
Text-On-A-Path

Scale

Here you can choose the scale of the path on the page. When Fixed is selected, the path will remain a constant scale at all page widths. When Flexible is selected, the path will scale to fill all available space.

Alignment

Here you can set the horizontal alignment of the path on the page.

Max Width

Here you can set a maximum width for the path on the page. Use % units to keep the path at a constant proportion to the page width. Use px units to set a maximum static width for the path – below which the path will scale along with the page width.