Some say the cleat should go further back to be more in line with your lower leg. The reasoning being that less energy is lost from the foot flexing to absorb the transitional forces.

But I think in the end, it comes down to what is an individual taste. If you are strictly comfort oriented, then position it where you like.

The spindle is behind the balls of my feet. When my oldest son recently started riding with me, he was constantly complaining about his calf muscles burning. I finally convinced him to move his cleat further back on his shoe just to relieve some of the lever moment his calf muscles had to overcome to keep his feet from flexing too much. He doesn't complain about that anymore.