The flare will tend to raise the Helmholtz frequency. If it's 4" long overall but flared at the end, it will act like it's slightly shorter, which will raise the Helmholtz frequency a little. On some speakers, this might be a problem. It might be best to know the exact tuning frequency on speakers with tight tuning tolerance requirements. In this case, the speaker is slightly overdamped and tuned low, so it is pretty forgiving of minor changes in tuning. I like them this way because it makes them forgiving of environmental factors and electro-mechanical parameter shift.

Overall, I don't think the flared end is going to help anything in this speaker because airspeed is low. On the other hand, it probably won't hurt anything either because the cabinet alignment is fairly tolerant of minor changes.