My desire for very sharp prints does not allow me to flip the neg over. In fact, I won't even use a set of BL bulbs to expose carbon prints with because of the loss of sharpness that results from such a diffuse light source.
The reason for this is that the emulsion of the carbon tissue is many times thicker than the emulsion of silver gelatin paper. Diffuse light has the opportunity to spread out within the emulsion and softening the image.
Enlarging negs with film of digitally does give one the opportunity to flip the image before making the carbon print.
I think my prints look (or feel) sharper than the negatives -- due to the additional apparent sharpness gained by the edge effects of having raised relief.