Will a reed always cut off the flow of air completely (as near as clearances allow)at an instant, which would happen if the reed was straight, or will it be curved relative to the surface of the reed block and cut off the flow progressively towards the tip of the reed?
If the later case is true would this affect the amplitudes of the harmonics.
For comparison I suppose that you could try a siren with holes on the fixed part that were the same shape as the moving part and one where the holes on the moving part were tapered?

I don't know who's going to try out these thought experiments:)