[JAlpert]

The probability of at least one vision tetra being only the center line is actually slightly lower than 50% because of the case where both vision tetras are on the center line.

There are 56 possible permutations of tetra combinations. 26 of these combinations include cases where at least one tetra lies on the center line. 30 combinations include cases where no tetras lie on the center line.

So, there is a 46.4% chance that a vision tetra lies on the center line at the start of a match (either do the brute force division or subtract the 100*(2/56) percent chance of two tetras starting on the center line from 50%).

Personally, the 3.6% discrepancy doesn't matter much to me, strategy-wise. If a robot can cap a vision tetra on the center goal at the start of a round roughly half of the time, it is probably worth it to try - on one condition. That condition is that no matter what, your robot puts the starting tetra for the alliance on the center goal regardless of whether or not a vision tetra lies on the center line. If a vision tetra is on the line, the robot puts both up. If a vision tetra is not on the line, then it puts only your starting tetra up. Either way, you start the round with at tetra on the center goal, so you really can't go wrong.