I remember one event when we were jumping a bullfinch (not named after me!!) and it was very tall. The horse didn't believe me when I tried to communicate the jump through and cleared the sucker.
Horses, through training and practice learn how to read your clues on approach to know what kind of effort to put into a jump. The solid elements used to be hidden in the brush, back in the day. Now, the solid element is very solid and visible.