Original purchased fare appears to have nothing to do with upgrade offer these days. From what I've seen, upgrade price largely varies with availability in the F buckets. It'd probably be more helpful if people provided the F bucket inventory rather than original fare. In this case, DL1254 is Z1, while DL2775 is D2, so DL2775 gets a significantly higher FCM price. Also, there's really no point in giving the mileage amount since it is simply the cash price minus the 7.5% US Excise tax at the rate of 1 CPM. Here's the magic formula to get mileage amount ( price / .01075 ).
Thank you for that formula! I was wondering where the numbers come from!