photoman,
Yes, I’m familiar with Rav Moshe’s tshuvah, but my own rav earned semichah from Rov Soloveitchik who pasked otherwise.
Trying my best,
Rav Soloveitchik and Rabbi Yosef Eliyahu Henkin paskened that a 40 inch high mechitzah is kosher l’chatchila. Rav Henkin also paskened that a mechitzah must be rigid, so some of the high mechitzahs I’ve seen would not be kosher according to his opinion.