Personally, I never got the same answer twice regarding the 'crown of the head'... But I did come to believe that it was either the very tip-top of the head or the skin at the border of the hair and forehead, in the mid-point, as in between the eyes.
I'd hate to hear that one was good and the other was bad, because I've done it both ways.
Ever hear about my companion and I being asked to 'cure' a Down Syndrome baby? We weren't successful.
As a kid, I had the bad luck to wake up from a minor concussion just as they finished the blessing and were wiping their fingers. Yes. I was a faith promoting story for many years to come. It still felt like I just woke up though rather than being delivered by the hosts of heaven.
Nowadays I like my olive oil seasoned and in a salad rather than blessed and on my head. Also, put a little black pepper, garlic and parmesan in it and dip a crusty bread. Anointing is optional.
One drop goes on top of the head. I carried around the standard Mormon-esque oil vial, a small metal cylindrical capsule about 3cm long and 7mm wide, that links to a keyring. It was on my everyday keyring I carried in my pocket with my keys. The lid unscrews and there's a tiny rubber o-ring seal. I dripped 1 drop unto the person's head, then placed my hands on their head on top of where the drop was and spoke the anointing part of the blessing (the short part). Then, I put my hands back on their head and spoke the sealing of the anointing part and the blessing (the long part).
But the drop of oil was tiny. It was almost nothing. I don't remember ever having to wipe it up, rub it in, etc. It just absorbs I suppose. Many people's scalps were already oily anyway. Most of them had hair to further wick the oil up.
But even on a bald head, one drop of oil just doesn't make a splash, literally.