The standard of sencha in Japan is Yabukita, a cultivar prized for its balance between savoriness and astringency, and grown in 75% of the tea fields in Japan
Consider also cold steeping or ice steeping (see Steeping Techniques).
Tea: 5 grams or 1 teaspoon. Time: 45-60 sec. Water: 70˚C/158˚F, 180-240 ml.
Tea: same. Time: 10-20 seconds. Water: 80˚C/176˚F, 180-240 ml (about 1 cup).
Increase time to 30-45 seconds or to desired strength.