"Lower the right foot to D to form a left walking stance toward C pivoting with the left foot while thrusting to D with the right back elbow, placing the left side fist on the right fist. Perform in slow motion. "

Why is the left side fist placed on the right underfist? Why not the left fingerbelly placed on the forefist (as in po eun). More generally, why are the hands brought together in certain movements,for example the backfist in Eui-Am, as this surely eliminates any chance to utilise reaction force.