I’m also not sure how small is too small for something to be detectable with current technology when it’s as far away as Mars, but i’m fairly sure a 6-12 cm diameter is too small. I think the smallest asteroids recorded are at least a meter or two across, and those were detected much closer to Earth.

This one was about one meter in diameter but that came as close as 12,600 km to Earth. Mars is at least 56 million km away.