This doesn't say anything (especially without face). Only the surgeon knows how much should be added (a good surgeon). In the ideal case, he'll know beforehand during the design. If not, he should be able to carve it during surgery. Only a few surgeons know to design the right dimensions. It's not only a technical thing, you need to be an artist and have much experience. It mostly comes down to millimeters, it should look as naturally as possible.
Depending on the face, the above difference can make a huge real life difference. If you have a small face for example, one should usually be more cautious with adding too much. For other people, one or two millimeters more doesn't make alot of difference. It all depends on the face.