Yes, i think that's fair too. Adding a slight fare increase by a stop over is equitable, but the 2X rate is a bit over the top. A bit of a bummer we can't do the longer stop overs anymore though. Hopefully CX will bring it back next year.

But, as a test, please try to book PVG - LON on a normal return fare. THen the "stop" over box appears in the bottom of the booking page. You'll be asked to then indicate 1-5 days stop over. But in the 2nd step you can actually extend this to as many days as you please. And you get the lower "D" fares. PVG to EWR/JFK doesn't trigger this box. A bit odd? wondering if this is a glitch or if it is something unique with Shanghai-London route. Customer service couldn't answer this when I spent 1hr on the phone trying to get a good rate on my Bali-London ticket.