That's another of the several small gripes I have about the Yamaha, it won't remember the text size. You have to set it every time you turn on the keyboard.
BTW, Korg does that too, but there are only two sizes to pick from. Good thing about the Korg format though is that it automatically wraps the words at the end of the line, so you don't have to be so particular about your line lengths when making the text file. If you have the wrong line length or text size on Yamaha, it just cuts off the line.
DonM