you know, I love John O'leary's website and his videos. He has some great thoughts and all, but his writing is so disorganized it's hard to make head or tails of him sometimes. In any case, the photo he's shown there are great examples.
The OP"s horse looks a little "hammer headed", meaning a very straight neck that goes up and ends abruptly with the head at a 90 degree angle to the neck, like a hammer. This reflects the shape of the neck vertebral double S curves, which in this case must be somewhat flattened out.
The goal will be to lift the lower part of the neck (that lower curve, which comes out from between the two shoulder blades), and lower and put more curve into the upper part of the neck.
I would start , as always, by asking the horse to stretch downward and forward, the so called "riding long and low" This is the beginning.