Batch-edit subtitle text frame width in Final Cut Pro?

Final Cut Pro 12.3 – Can I change the text frame width of all generated Subtitles at once?

I've generated subtitles using Modify → Generate Subtitles. I can change the font, size and style for multiple subtitles, but I can't find a way to change the width of the text frame (the wrapping area) for all subtitle clips simultaneously.

Saving the subtitle as a default style doesn't seem to save the text frame width, only the appearance.

Is there a way to batch-edit the subtitle text box width, or is this currently a limitation?