Dishing flip flop or spacers behind sprockets?

A EF: Perhaps an uninformed / naive question, but are you sure that the distance from centre to shoulder is the same on the freewheel side of the hub as it is on the fixed side? By centre, I mean exactly half way between the locknuts, not half way between the flanges.

Example:

• If centre to shoulder on fixed side is 35.6, your chainline will be 35.6 + 6.4 = 42mm
  
• If centre to shoulder on freewheel side is 34.11, your chainline will be 34.11 + 7.89 = 42mm
  
  

Now, I am sure it won't work out this perfectly, but if centre to shoulder measurement is different on both sides, it will impact how much spacing you need behind the Surly / Andel.

Perhaps I am being a bit dim (quite possible) and missing the point. If so, please ignore.