Curve the bottom edge of the block from the centerline waist mark to the lowest front mark. The descent should start a short distance from the centerline, but should not become steep until it is half-way from the centerline to the front side. The meeting point for the angle used to create the curve in the waistline is at the half-way distance.
Another way to look at this curve is to divide the horizontal distance into thirds. The first third is a slow slope. The second third is a steep slope. The last third (which can appear to be less than 1/3 because of the angle of the front edge) is a slow slope, nearly perpendicular to the front edge.
Next find the point where the top edge of the front half starts to curve into the armpit. This point is above the angled intersection of the waist line. In other words, if you draw a line parallel to the center line upwards from the point of the waistline angle, make a mark where the line crosses the top edge. Start the curve to the armpit from this point.
This block does not include shoulder straps, so I want to keep the top of the back below the shoulder blades. Square the ruler to the back side at the horizontal bustline and draw a line.
Smooth the top line from the back side to the armpit.
Darken the outline, and strongly mark the centerline. I recommend using a pen to make it permanent and easily visible underneath other paper. This is now a basic conical block.
The block variations are drawn in pencil within the inked basic block.
This variation will cause the corset to hug the torso to the underbust, and then curve out to the bust. Create a curved underbust line and measure to the ¼ underbust measurement. Draw a new front line from the bottom front to the underbust, and then curve it out to the curved bust line.
For a more scooped bust, start the top edge part-way between the curved bustline and the straight bustline. Increase the height of the top edge in front of the armpit. This will expose more bosom at the very center front and create a more dramatic sweeping line.
To create more squish and upward thrust, bring in the top of the front side and extend the height by the same amount. If you bring in the front without increasing the height, it will just cause spillage. Do not bring the front edge all the way in to the ¼ underbust measurement.
If you want a higher back, curve the top edge up approximately half-way from the centerline to the back edge along the bust line. Be careful that the height of the back is either low enough to be completely free of the shoulder blades, or high enough to cover them at all times. If the height is in-between those two, it will rub the bottom edge of the shoulder blades as the wearer moves.
Making a Usable Pattern
The block pattern can be divided up according to the piecing patterns of just about any historic conical stays or bodies. Just divide up the space according to the pattern being imitated, and add seam allowances and other needed marks.
I currently have illustrations of converting a conical block to the following styles of stays or corsets: