In an exponent which itself contains exponents, does the appropriate level indicator get used before the fraction line and the closing fraction indicator? See attached Fraction.jpg. That is, did I braille the equation correctly? (Sorry, I couldn't figure out how to show simbraille)
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."