This is a g reat post. I've made hundreds of whistles similar to this, but patterned after the older Iverson whistles. The only functional difference is that your wedge is recessed and I'm thinking easier for some to use. I like your comment about the sharpness of the hole edge too. That is certainly key.
I've always used a drill bit, with a dowel inside to prevent tearout, then used the chamfer bit to clean things up, but I'm going to try your way this weekend.
Are you sure that the hole depth doesn't matter? ie: the distance from the second hole to t he end of the bore? It changes tone for me, if it is too deep.
Thanks.