You have to decide if it is more worth to you to put the tetra there or not. For example, some robots may not be able to simply push it aside, they'd have to lift it. This would take some valuable time which could have been spent loading. However, how much is it worth for your robot to put it there? If you are a "box on wheels" robot with pushing capability, cornering the tetras into their loading zone could be to your benefit, but if you have to spend time lifting them and placing them, there are more efficient forms of defense.
Your strategy team and you can decide that
Just remember, your actions can save or waste your own time as well as other team's times.