This actually reflects a Virgin Atlantic devaluation. They used to award 2X miles by distance on all Upper Class fares, but they reduced this to 1.5X on deeply-discounted fares a few years back.
To get a more accurate picture you also need to look at the Tier Points that you would earn on these flights, the elite status bonuses, and the miles earned if paying with Virgin Atlantic's affinity MasterCard. The $1,222 fare will generate another 3,666 miles through the VS MasterCard, but the $6,812 fare would generate 20,436. Virgin Atlantic has designed their program to reward the engaged flyer (earned elite status, carries credit card) more than the one-time buyer of a premium cabin ticket.
True...though I guess this also stands out as odd in its own way (the card generating roughly twice the miles in such a situation as the actual trip...I'm used to a ratio that's either around 60% of base earning [Hyatt, Virgin America] or equivalent to [Amtrak], but not substantially in excess of).