Mass of the punch may be increased by using muscle tension to add the masses of the shoulder, torso, legs, and feet to the mass of the punching arm. Generally, speed decreases as effective mass increases, but, by using a sequential application of forces, such as arm, then shoulder, then hip snap, and then leg thrust, the fist is snapped out similar to a whip, without adding mass that may slow speed of the punch. Then, at moment of impact, the body tenses and adds the mass to the punch.
Focus is when a full-power, full-speed technique is aimed to terminate a point in space. Focus is not just terminating the technique at the point in space; it is also a simultaneous contracting of all muscles to add all the power and mass of the body to the technique. Maximum power occurs when all muscles of the body contract at impact. Since the impact force of a technique equals the mass times the acceleration of the attacking weapon, to reach maximum force, you must be loose and relaxed as a technique starts and progresses so you may achieve maximum acceleration, and then contract all the muscles to achieve maximum mass. Since the technique stops at the point of focus, maximum force of the technique occurs at a point just millimeters before the point of focus. After maximum power point, the fist is decelerating. Without the contraction, maximum power is not reached; therefore, if an opponent moves into a technique that was intended to stop just short of contact, the attacker can lessen the force of the impact by not contracting into the technique. When sparring, the point of focus is just short of the surface of the chin, so the opponent is not harmed. In an actual attack, the focus point is internal of the chin, so that fist is at maximum velocity when if strikes the surface of the chin and thus strikes with maximum force.
Taking all this into consideration, which punches harder, a large person or a small person? The large person has bigger muscles and more mass, but it requires more muscle power to move the greater mass so acceleration and velocity of the punch is reduced. The smaller person has smaller muscles and less mass, but the acceleration and velocity of the punch is greater. This, striking pressures of the two punches may actually be equal. The striking force of a speeding bullet and speeding locomotive may be equal, but which would you rather be hit by?