You can put a tetra on top of the goal with out having to go 2 1/2 feet out
Have you not thought about going over the bottom bar then dropping the tetra unto the goal. So as long as up the human can place the tetra far enough on the robot arm and the arm is in the center of your robot you could put many tetra on at one time and place them all on the top at once without flipping. 5 tetra is not un heard of.
To give you what we had in the past
http://www.valleytech.k12.ma.us/robo...1Robot2001.jpg
this arm went up 14' to place that ball on. It is all about keeping the CG low enough