I found this interesting enough that I found the three guitars that i have with volutes, looked at where they are, and played them. One previously mentioned has the peak of the volute around 3/8" above the face of the nut. Very comfortable, and my thumb just rests on it's slope when I play an open C chord (I have fat fingers and big hands, and I need to really lower my wrist and get down behind the neck so the G-C-E notes are not muffled). Obviously I carved it to suit my big clumsy hands, I guess! My Paul Beard Special Goldtone dobro has a volute as suggested here, peak directly behind the nut, and it definitely interferes with my thumb in that chord. Odd that I never noticed it before but I rarely play open "cowboy chords" for that very reason - my fingers don't fit. Finally a Fender style neck on a Telecaster style guitar (a Godin TC). The very design of the Fender neck, sawn out of a slab of maple, has the back of the headstock on the same place as the heel that bolts into the body pocket, and the neck carve puts a semi-volute around 1/4" past the face of the nut. So three more place-points for the study...
