oh this was also my party... we all experimented with facing towards/away, moving or standing still, and then just bumbled through without actually learning how the mechanic worked
my fiance kept telling me to get 'behind' the minions and i did not realize he meant in relation to the boss so i kept screaming I WAS BEHIND THEM but no no i was not
I forgot about the existence of Rathalos mechanics.
And this reminds me that I still have to do this week's loot farming, whoops.