Tried searching for this but couldn't find anything on point:

Booked IAD-BRU-IAD in C both ways for $8,xxx.xx. Flew IAD-BRU. I'm now unexpectedly in AMS. I'd like to fly home from AMS and not take the train down to BRU. So, I called UA's Netherlands number (routed to the ICC), and was told it would be ~$700 in fare difference to switch my return from BRU to AMS. No complaints about that part -- I get going from a round trip to an open jaw will have fare consequences.

I next asked how much I'd be refunded if I cancelled the return leg (BA's got a great one way deal from AMS). I was thinking a refund would be something like 40-50% of $8xxx. To my surprise, the ICC said the refund value of my BRU-IAD C ticket is under $700+taxes. How can that be? The outbound leg is valued at over $8,000, and the return leg at less than 10% of that? Is this normal for the return legs of high dollar full fare tickets? Should I call the U.S. 1P desk and have them sort it out?