Forehead muscles and hair transplant

If your doctor said that what you want may look unnatural, it would be wise to listen to your doctor.  A very low hair line can look unnatural.

It is true that you do not want the hairline to be placed too low.  Bringing the hairline below 6-7 cm from the brows in a man or 5-6 cm from the brows in a woman starts to look very odd.  Everyone's forehead folds are in different locations, so the placement of the hairline relative to the folds should be judged on a case by case basis.  In general, the most prominent horizontal forehead folds are in the mid-forehead area and the hairline should not come close to these folds as it will look unnatural. 

The highest crease of the furrowed brow is my limit to lowering the hairline because then the hairline moves when you speak and becomes actively involved in your expression.  Taking it to the highest crease is reasonable