Of course they are correlated, my point is a 50% fall in crude does not mean a 50% drop in JETA1 price. From your chart you can see where crude has fallen over 50% in the past year JETA1 has fallen from $2.85 to $2.40 or about 15%.
I believe Jet A1 now runs at about $1.30/gal. It was $2.60 when crude was $95 so has caught up - you obviously get a lag and there's a fixed cost of refining but the idea that the fixed costs skew it dramatically is rubbish.