Maisie Williams - 5'1" – and Gwendoline Christie – 6'3" – rehearsing
So I'm 6'3" and when I did sword sparring with shorter folks back in the day it wasn't that they were faster or more agile that was the problem, they just never seemed to run out of energy. I really had to slow down my movements and change my strategy to keep up with them. Expend a large amount of effort only when I was sure I could end it or over power them.
Also when you have that much size on a person as Christie does over Williams you really have to hold back. If the smaller person manages to hit you it's going to sting but if you, as a larger person, go for a big swing and connect on them you could do some damage.
Of course they are rehearsing and don't do actual contact so it's a bit different but Christie has to watch herself a bit more than Williams does.
Nice. Of course it's hard to tell from a rehearsal, but the fight choreography looks pretty good to me. (Granted, I was an at best mediocre fencer, so I don't have an eye for the finest points.)