Hi,
in a previous topic, I presented a method to wrap a sketch around a cylinder with known accuracy, saying the process could be extended to a cone.
Accurate method to wrap a sketch to a cylinder
Here is the adaptation of the method to wrap a sketch around a cone. In first approximation, accuracy is the same as for cylinder.
The process is roughly to slice the cone in sectors (piece of cake) and place them in such a way that they project onto a plane as a perfect 2D sector.
To do it easily, it is convenient to place the cone section with the oblique line in vertical position.
An odd number of slice is recommended : 9 or 15 are good choices.
Then, as for the cylinder, the cone is built after the sktech has been projected, using the align tool.
Of course, you will have to create the sketch in polar coordinate 
(polar effect on some app can help) and, as for the cylinder method, ensure that no control point of a spline will project too close to an edge of the flatten cone, or the extrusion may fail. Extrude before doing the union of the slices or it may also fail.
This method is a workaround for those who don’t have access to wrap or emboss tools but still occasionally need to accurately wrap a sketch around a cone on their tablet.
It can be adapted to a certain extend to free form shape 
Your behavior makes me feel like I am an idiot