Okay, so, you're saying that the game design, and the invicible 'border' that determines if a slip stun will happen or not. Is my fault, and also, determines my skill level? Okay, work.
There seems to be an invicible 'border' that determines if a slip stun will happen or not. While it reaches till the end of the river on the left side (where the crocodile is), it does not on the right side (where the flamingos are) and rather seems to end two meter in front of it, meaning only like 60% of the river is slip stun area.