If you're talking about a standard thruster, it seems to me the top 4-8" of the board really exist to lower the entry point and keep the board (& you) from pearling on steep drops. Bringing it to a point just keeps the volume and weight down since the nose isn't providing you any flotation and most of us aren't riding that part of the rail. However, the sharp point that characterizes the nose of the modern thruster seems largely stylistic.
Each shaper seems to have a characteristic way of shaping the nose - sort of like a signature. For example, Channel Islands noses are a more rounded than Rusty's. David Craig, a local shaper here in San Diego, puts about a 1 cm flat spot on tip of his noses. While it's largely aesthetic, it's easy to underestimate the value of that. I tend to surf worse on a board if I don't like its looks. Then again, I have old boards that are ugly and beaten but that I did all the damage on and I love to death (and still ride great - brown spots and all).
In conclusion, I'm talking out of my ass. You will find almost everyone discussing the nuances of board design who isn't a shaper is doing the same thing. If it goes for you, stoked. If it doesn't, move on.
I should want to cook him a simple meal, but I shouldn't want to cut into him, to tear the flesh, to wear the flesh, to be born unto new worlds where his flesh becomes my key.
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