Precision of "Convert entities"

Hello, I have a precision problem (curvature that goes peanut at the ends) in sketches when I want to " convert entities " on a surface edge which is a spline of some kind. I should point out that the surface whose edge was converted was created from 3d style splines. Is the accuracy of this tool adjustable? Or should I only use curves driven by an equation?

Hello

if I understood correctly; Would you like to convert a sketch to use in another function? If this is the case no need, you can use the 1st sketch just by selecting the function and then the sketch then it will be shared.

Hello
The curves created by conversion can go into peanuts by extending them but in fact it is very precise. The spline follows the same curvature that it had before extension. But it is difficult to judge on the image shared.