There is no right or wrong answer to your question. Windshield height is a matter of personal preference.

Most people prefer to look over the shield, as do I, but that is not to say that you shouldn't look through it. It's really up to you.

 

I look straight through my 24 inch Clearview recurve shield. Love it. Have to make sure there's plenty of fresh RainX on it before heading out on trips. Still enough wind to blow the hair and know you're on a bike.

 

+1

One of my rider friends has a windshield that is taller than his head, and he loves it because it cuts down on so much wind. To each his own ...

 

Black and Director are correct.
There is no "should be" height.
Because of wind buffet when I wore a helmet, I got a 2 inch over stock windshield on my EG. Stock is 12" , mine is 14".
I've had this windshield for about 35k miles and love it.
Even in a down-poor (day or night) I don't look over the shield, I lean forward closer to the shield to keep rain off my helmet visor or glasses.
I've never had a problem looking through the taller shield.
If you do get a tall one, be sure to get clear without any tint.

 

I bought a couple old windshields at a swap meet. Little by little I cut one down an inch at a time until I knew the height I liked. Then I cut the second shield exactly where I wanted it. I use that one. I cut it with a coping saw and sanded the edge to a nice finish. The best part was that I only paid $7. a piece for them.