Characters like Ammy, Magneto, Akuma, Nova have bigger grab ranges than others.
The other thing is how good is their jumping H. If it is their universal aerial attack ... then they will be option selecting air grab which will net them more air grabs.
It's not the grab range, its the fact that he (and the other 3 characters you mentioned) can fully capitalize on a grab with no help which many characters can't do. Also I'm pretty sure Nova's grab range isn't any different than any other character of his size, in fact, I recall something about characters like Ammy and Felicia having an easier time throwing because they themselves have a smaller hit box making them harder to throw.
Chris is another character who is great at utilizing throws, he can get full combos off of either a ground or air throw with little effort.
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