Bad! Very, very bad! Just don't do it...
Theory I've heard is that circulating current is more or less directly proportional to the # of taps by which the reg is offset from neutral; anecdotally, even on a single tap offset, the circulating current is reported to be so considerable as to be, as one lineman so eloquently put it, "ugly," to the point that my utility's standing instructions stipulate that the last resort to switching an off-neutral-tap regulator into service is to take an interruption on the line, open the bypass sw and close the reg isolating switches off pot, then return line to service.
Don't know if this helps or not...
CR
"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]