It’s all about the shape. Vizard was big on 30 degree seats.
While you can’t ignore what goes on at .100 lift, the valve spends so little time at those lower lifts that it’s really hard to make big improvements in power focusing on flow down there.
How much flow can you gain when the valve is .100 or .200 off the seat? The curtain area is so small any gains will be small and may affect flow at lifts where the valve spends most of its time.
You also have to consider what the shape of the flow is getting around the valve with a 30 degree seat. Any time you flatten the seat angle, you force the air to head towards the chamber wall rather than into the chamber.
Visualize what the shape of the flow would be like (or draw it out if you like that better) With a 30, 45, 50, 52, 60, 62 or even a 65 degree seat.
The steeper the seat the more vertical the flow pattern around the valve is.
