[kamocat]

I'll share my strategy in this case, because I think it will help the overall safety of the competition.
For the most part, aiming at the closest target is what you want, because it's also the target that can most easily reach you. However, you also want to aim only at targets inside the arena. How can you tell where the edge of the arena is? The white flooring ends.
So, in your aiming VIs, you can disregard targets that are further away than the edge of the floor. Obviously, people are a lot larger than the targets on the top of the trailer, but you can tell where they are by where they touch the floor (or if they don't, as the case may be).