Create a copy of your basic block and draw the neckline first.
Lower 9-10cm from shoulder point along the armhole (same measurement on front and back), then:
- on back go perpendicular to center
- on front, measure up from your nipple point to have the neckline of a depth you like. Draw the neckline, then widen the shoulder dart by 1cm at neckline.
This little trick helps the dress sit tighter on the chest.