Everybody finds out the same thing: The place for the key is at the height your elbow falls if you let your arm drop when you're seated in a chair. That height varies with the height of the person and the chair adjustment, but it averages 28 to 30", which is why that's how "high" desks are.
The place the key needs to be is back towards the rear of the desktop, at least by the distance between your fingertips and your elbow. Again, that varies with the person. For me, it's about 19". For somebody very tall, it would be more.
The reason the key needs to be that far back is so that when you send code, your entire forearm can rest on the desk, including your elbow, and your arm will naturally "fall" across the desk to where the key is located. That's the most comfortable sending position, and the one virtually everyone wants to use.
It's very difficult to send code on a desk that's too "shallow" front-to-rear, or with a key that's located too close to your body.
WB2WIK/6