If you are not balding and were born with a high hairline, you DO NOT want a hair transplant.
I was where you are. My forehead from what I recall measured around 10 cm from hairline to nasion:
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This was way too big and I have hated it my whole life. A few weeks ago, I got it fixed, but not by transplants. By forehead reduction. Forehead reduction is the only procedure that can eliminate a large amount of forehead while retaining natural density and hairlines.
eg.
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A transplant will never match more than 50% of your natural density. DO NOT ATTEMPT TO FIX IT THIS WAY. It won't look right.
The best doctors probably in the world for this are Dr. Fleming and Dr. Mayer in California. They have extensive experience with all sorts of advanced scalp procedures. I went with Dr. Fleming and I've been extremely happy, though I'm still healing.
If you want more than 2 cm reduction, you will need a balloon expander implanted first, which you will have to expand over the course of 6-8 weeks to stretch the scalp more to get more motion.
I had 5 cm removed as they took a bit of the frontal hairline out during the recontouring process after 500 mL fluid expansion. My nasion to hairline measures around 5.7 cm now which is relatively compact nicely proportioned to my face.
Rahal quoted me 2400 grafts to lower my hairline which would have created a horrible outcome. It would have looked horribly thin and abnormal.
Read up on this procedure and think it through. The only warning with this procedure is you can't go bald after it, or it will leave a linear scar across your forehead exposed. So be prepared to take heavy drugs if needed should you start to suffer from male pattern baldness or don't do it. You need to preserve the appearance if you do go ahead.
Just curious, what's your measurement with a tape measure from nasion to hairline?