DY,
Thank you for correcting me about R’Moshe’s shitta on mechitza by a wedding. However, I should point out that the teshuva you cited is holding that a mechitza is not required, it is not clear what R’Moshe would hold about separate seating.
Furthermore, R’Moshe’s rationale is that by a wedding it is closed group, primarily family, and therefore kalos rosh is more easily controlled and prevented. It seems to me that there is a question of metzius here and that judgment needs to be made on a case by case basis.