Two variations in foot position I have been taught in formal instruction. First, striking with the heel. Later I learned to strike with the outside edge of the foot, the "blade of the foot". I was recently shown another variant from an old school TKD friend. Instead of striking with the heel or blade; striking with the extended ball of the foot. A bit like a sideways front kick. I can see uses for each. The heel is a tough spot, hard to damage and no toes in the way. A great choice for strict placement on a small spot. It is my choice for a shot to the bladder or solar plexus. The blade, I use it to gain more full contact and either push away the opponent, or bend them over a bit with a low gut shot. It also gives me an additional two inches ish of reach. With an extended foot (the ball) , I only have done it while executing aerial side-kicks when my opponent was quick and I needed still, a few more inches of reach. The striking area is smaller again, but the toes are exposed and vulnerable. What do you do, and why? What do you think?