The reason you are being offered 20's+ is Colin Tizzard has absolutely no intentions of running Native River.
Without looking you may well think the King George is the more valuable race but it is not. The prize money is exactly the same.
There is a possibility both Thistlecrack and Douvan could turn up at Kempton there's no chance of that at Haydock and there is that mil to consider
Against that on his first race last season Might Bite was beaten fair and square at 1/2 and that is probably what is worrying NJH and pointing him towards an easier target
Sizing John looks the safest bet and 3/1 could look huge on the day.