For comparison, my wife is 5' 7''. Her handlebars are even with the seat. I just measured that there is enough space to drop the bars about two inches.

Then too, the fork compresses when you put weight on it. She probably has her bars 3/4 of an inch or so below the seat when she's on the bike.

I wonder if anybody considers the compression of the fork in setting bar height. I know I don't, yet it would seem logical to do so. At least then I'd be consistent between my road bike and my mountain bike.

Some frame designs have a higher bottom bracket than others. That increases the seat height. There is 3/4" difference between the BB height of my old touring road frame and my new cyclocross road frame. I don't know about mountain bikes.

Al