During a hair transplant, hair follicles are taken from one area of the scalp (the donor area) and transplanted to another area (the recipient area). The success rate of hair transplantation is generally high, but there are some factors that can affect the growth of the transplanted hair. One reason why grafts implanted on the skull may grow back later than other implanted areas is due to the blood supply to that area. The blood supply to the crown and vertex area of the scalp is generally less robust than other areas, which can make it more difficult for the transplanted hair follicles to thrive. Another reason could be the angle and direction of the implanted hair. The hair on the crown and vertex area tends to grow in a different direction than the hair on the front or sides of the scalp, so the transplanted hair may need to adapt to a new direction of growth, which could take some time. Finally, the density of hair in the donor area could also affect the growth of the transplanted hair. If the density in the donor area is lower, the transplanted hair may be less robust and take longer to grow. It is important to keep in mind that hair growth after a transplant is a gradual process, it can take several months for the new hair to grow to its final length and for the results to be visible. It's also important to keep in touch with the surgeon and follow the post-operative instructions provided by the surgeon, including avoiding strenuous activities, avoiding sun exposure and keeping the scalp clean to avoid infection.