Please post a photo of your green, scaly thumb in the position you described, TB.
When playing a barre at the (3-4) wider frets, the lower part of my thumb's pad is on the skunk-line, the joint between the distal and middle phalange being slightly below it. My thumb pad is placed vis-à-vis my middle finger.
As I work my way up the fretboard my thumb works its way gradually more towards my index finger, so that by the 7th fret, my thumb and index finger are in opposition.
My wrist is straight in both planes.
I don't know if you have been involved in some bizarre moped accident, TB, but getting your thumb an entire fret away from your barring finger, playing an F# perhaps, sounds like a congenital defect of the kind usually only found in the more remote areas of the Appalacians