Because my spherical -400 mesh will hardly light even with KClO4. That's why I think it's flake.
I'm a bit confused. Flake is the easiest to light, next is granular, and the hardest to light is spherical. While Flash Aluminium (nano sized atomised, dark flake ect) ignite easily with Potassium perchlorate, and some of the less fine flakes like bright flake light fairly easily, all other Aluminiums will be very hard to light mixed with just Potassium perchlorate. The addition of some Black powder, or an organic fuel like Red gum will make it much easier to light.
So, while -400 mesh is quite fine, if it is spherical, I am not even slightly surprised that you find it hard to light with Potassium perchlorate. What you are experiencing is normal, and I see no reason that it would be flake.
and about the boric acid, i dont thing u need it, this mixture has no sulfur, and it had lot more fuel then the oxidizer so i dont think its senetive one, but why taking risks?? try it, tell me if its having any influence on the stars
Boric acid is to prevent or reduce the corrosion of Aluminium by nitrates. However as your experience shows, it does not always react without boric acid. However if the mix heats up and smells of Ammonia, this is when you know that you should have added the Boric acid!
How fast do your stars burn?