Horses are measured at the shoulder in “hands”. A “hand” is 4 inches. A good sized horse is often 18hh but can be 20hh or a little more. 18x4=72" == 6 feet = 183cm.
The average height of a man in the USA according to Wikipedia, is 5’ 9" for men. “Tall” would be 6ft ~ 6’ 2" - for a man and gigantic for a woman.
This means that a “tall” man would be looking up at a “good sized” horse’s shoulder and a saddle horn would be measurably over his head. And that’s not even what it is with character max size in CE. In CE with character “middle to Max height” you’re about eye-level with the horse’s shoulder.
My character is also max height and the horse is shorter than me. I don’t have to look up even to see the saddle horn and the horse measures to about my mouth or chin. I’m either very tall and the horse is average or I’m a giant and the horse is too. Take your pick but the horse’s height feels very natural to anyone who has actually been around horses. 
Shire Stalin, 4 years, 18hh.
6 years, 18.41hh
etc.