I have heard many 'theories' on how far back the distant mic should be. Typically I hear 6 feet, 10 feet, or even the opposite corner of the room. In a really big room that would be silly, of course. I experiment until I hear no phasing issues. But here's another interesting recording technique I stole from Steve Cropper (keep in mind his tone is pretty clean). He claimed putting his combo amplifier in a corner of the room, angling a piece of plywood behind the amplifier against the two walls, and placing the 'close' microphone in a sweet spot between the open back of the amplifier and the plywood, was his tone recipe. I haven't tried it, but I suppose it makes sense. What I do know is that I kept two e609 Silver mics, and they seem consistent. They also seem to have that mid hump. But then the 'new' Mexican SM57's also have that mid hump. In my collection of USA and Unidyne III 57's, they all seem smoother and have a flatter response. Now if you take out the transformer, that's even a different sound. So that's the can of worms as I see it from here.