This might help you think how to set up the FSM.
First detect the position of your character (For example I want to limit the Y movement)
If it reaches the max or min value send it to the appropriate state (High Low state)
Then use Float Clamp to clamp a variable of the Y value of your character (every frame)
Then use Set Position again, using that variable (every frame) to lock the character in the high or low value you set
Sorry I'm not at my workstation so I just typed it up. See if this helps.