Originally Posted by
cupsandsaucers
Oh ok. I think I follow. So it's assuming people from London will want a direct flight. However from Glasgow I may be tempted to fly direct on another carrier, ergo they tempt me to BA with a lower fare? (overall)
Bingo. However note that BA release at 355 days, and many airlines release seats at 300 or 330 days. So the full competition effect will not be in these fares.
On the other hand, if you start from INV and go IAD but return from BWI instead, it's only £777 in WTP.