Katrina,
I would transcribe the print you shared just as you have transcribed it. You’re right that the level must be specified for a fraction line or fraction indicator that is preceded by material on a different level.
⠐⠮⠩⠤⠠⠿⠣⠭⠻⠑⠘⠤⠹⠨⠭⠘⠘⠆⠘⠌⠆⠨⠎⠘⠰⠂⠘⠘⠆⠘⠼⠐⠙⠨⠭
“modified integral with below it negative infinity and above it x. Then e superscript negative fraction xi squared over two sigma-one squared [end (superscripted) fraction]; base-line d xi.”
Thank you for the question!
–Kyle