I think Talhoffer may have been beaten or had some very poor experience with people in his past, as he reacts very strongly if you make sudden moves towards him, or sometimes its enough just walking with a bit to much energy. And especially if you have something stick-looking in your hand and is coming toward his rear. This is nothing you want in a warhorse, and also its not very pleasant for him to react so strongly and being on edge.
To work trough this I started with an excercise where I press against him, but the thing is, i want him to push back, and not yield. In the beginning I was just putting my hand on his shoulder and rewarding when he didn’t yield. When he understood that I started to press a little and rewarding when he pushed back. Eventually I started adding to back up and add to move towards him. I have been doing this a little before, just rewarding that he doesnt flinch, but now it went so much better. Because now I had rewarded the impact, the pushing back, so he wanted me to come close so he could make his little shoulder push and get his cookie.
I like to think that its like when you let a kid win over you when wrestling. The kid nows that you are bigger and could easily bet him, but still get the feeling of being invincible and gets a confidence boost. This excercise gives the same feeling to the horse.
As with all things that can be potentially dangerous for the human, like rearing, kicking, shoving, its not suitable for all horses. Some horses will find this a little TOO fun to be shoving people around, so one need to take into consideration the type of horse one has.