Mark - To be honest, I don't know, BUT suspect it has something to do with paint pooling in the tip, other brushes I have appear to get a slight vacuum just inside the tip and blobs of paint can settle and dry here, so maybe these 'flutes'!! relieve that vacuum. Saying this, these still get some paint in there, but not as much as some. I think I tried an Iwata tip on it (same threads) or you can spray without it if you want- this is supposed to give even finer lines etc- BUT it also exposes the needle tip to being easily damaged. The thing that suprised me is, you can buy parts for them, which is a plus.
I keep calling it the 'Tip', but really it probably should be called a cowl, cap or hood- sorry if I have confused anyone. pete