The career profile of a horse is often the best 'tell' to what caused an outlying run, and as a tool for predicting if or when it's likely to happen in the future.
My take on the above 2 is:
that SOAV is a speed horse and though his Ascot h/c win was in a good (relative) time, the ground was pretty quick, they went no great pace early, and he simply had far too many gears for horses since proven to need further. He didn't get that luxury in the Xmas hurdle (hard to believe the ground was as bad as connections painted) and the searing pace set by Blue Heron had him taken out of his comfort zone a long way before the finish. Should BH repeat the exercise today, I'd bet on him performing similarly.
Silviniaco Conti is - as his trainer pointed out a while ago - "just a galloper", and though reported to be suffering stomach ulcers at the time, holding him up of a moderate early pace in last year's GC was never going to do him any favours. I'd still maintain he was outsped in the closing stages; connections have learned from that, and cheekpieces and more positive tactics are likely to ensure there's no repeat in this season's renewal.