How does one define the price of the ticket?

If the itinerary is AMS-CDG-XXX, the pricing of the ticket will be based on the AMS-XXX route. Therefore it is pretty much impossible to put a price on the AMS-CDG segment? In some cases, when bought as a separate ticket, AMS-CDG might have been even more expensive than AMS-CDG-XXX!

Of course, the above assumes that the 'base fare of the ticket' means the base fare of the segment. If I have an AMS-WWW-XXX-YYY-ZZZ-AMS itinerary, I doubt I am entitled to 30% compensation of the entire base fare when downgraded during AMS-WWW only.