This was done so that teams would utilize both forechecking and neutral zone play at the begining of the game. As the game progresses, a team may neglect neutral zone play and forecheck more, if it is losing or vice versa.
If you're playing against the Bruins, you need to be wary of both their forecheck, and their infamous 1-4 neutral zone trap as the game begins.
I tried NZ-FC at 0, and that leads to the no forechecking issue. I tried NZ-FC maxed, and that leads to too many odd-man rushes out of the gate. Hence, 5 is the best value.