I think the fact that it's 5 instead of 6 solely b

I think the fact that it's 5 instead of 6 solely based that they don't know when or how long it would take to get a 6th patient. To ensure they have the top-line data ready for the conference, including analysis, they need to cut the trial as soon as the 5th enrolled. Enough data points for the 3rd cohort, and still done in time for conference. I do also believe that better results will be seen in 3rd cohort.