The fda requested the investigatory mono trial find a group responders above 70%. They have done that with 525mg and 700mg. The fda has approved previous drug combos with that efficacy, even maraviroc combo below 70%. With requiring a new mono trial, we seem to be in a similar situation with mono as we are with combo, current results should be good enough for approval, but the fda is pushing for the best possible results instead of accepting results that is already better than previously approved drugs.
Maybe that is why the fda letter said they adamantly want to approve both. Sine they have already past the bar above the minimum threshold for approval.