Moves 5 to 10 of Heian Yondan can be very difficult. Height is not important, to the knee or groin is brilliant.
There are several applications for these two uraken uchi (backfist strike) and yoko geri keage (side snap kick) in Heian Yondan, but we will use them as two strikes.
From moroto uchi uke, the left kicking leg should lift immediately, with the knee pointing the way you are kicking (to the left) and the bottom of the kicking foot, facing the knee of the right supporting leg, try not to drag the leg accross to this position.
Both techniques go at the same time, with the uraken uchi hitting just before the yoko geri keage. Be sure and snap the kick back vigorously.
Here is the full Heian Yondan Kata Tutorial.