Yedrow, good looking Waterfall.
I, too , am a ^6 potter, working with MC6G glazes as well. I get good looking deep, complex surfaces and great satin matts. Not many people around here down fire, but I think it is a major reason my glazes look good.
I am having some trouble with slight pitting and cheezy surface. More with speckled clays , but some also from white clay bodies. I drop from peak temp to 1900* at 500 * per hour like the book suggestes, but am wondering if that is to quick for that glaze. Don't pits come from cooling too fast before that bubbles can heal over?
I fire pretty much the same way you described. I soak for about 10 to 20 minutes, depending on where the 7 cone is. I don't have any problem with pinholing or pitting, but I only use three dark clays and one white body. I know the glaze is 'frothing' around peak temp. but that goes away as it cools. I drop temp at or under 500/hour. I would slow that down were I problem solving the issue, but there are much better glaze people than me here for you to get suggestions from.