Originally Posted by
3544quebec
That's a roundabout way of saying that like me you have no answer to the specific question the OP has asked ie how that calculation is made and where he can find the rules for that calculation
That's saying that it won't be, as proposed by the OP that it wont be a refund of ratio of distance travelled over total proposed travel
(quote from OP : For a partially-used ticket, I believe I’ve always received pro-rated tickets (refund in proportion to the distance of segments flown).
What it will be is a calculation for a business class ticket for the journey undertaken, which unless it is very close to start of journey likely to be close to zero