There is no such consensus on Fortive Patah (not Patach) in terms of positioning! ; it is not considered a specific punctuation, subsequently no dedicated unicode.
At the end of a word the consonant Hebrew letters: He, Het & Ayin would get different pronunciations after a “vowel-ed” letter with Shoroq, Holam, Hiriq and Tsere, where irregularly “Patah” does not show underneath those letters at end of a word anyway. Not alike Biblical writings, modern Hebrew printing kept the same position for the so-called “stolen Patah or sneaky Patah” פַּתַּח גנובה
Anyhow if you wish to assign special positioning for it I’d suggest a SUB OT feature based on an extra 3 ligatures for: Patah & He, Het & Ayin.