I have a similar setup, Madstad bracket etc..
I have 2 holders on the bike.
My main holder goes above the dash, and I think that's where it needs to be if you rely on visual directions.
I have a 2nd holder on the bars that is just there to hold & charge my phone, but I have used that for Sat Nav too.
To mount the Sat Nav above the dash I made up a bracket which consists of 2 alloy fingers and a short length of old handlebar.
The only thing to be aware of, when mounting a Sat Nav above the dash, is the airflow. A very chunky Sat Nav can cut the air coming through from under the screen, which can lead to a return of the buffeting.
This is no issue with my Garmin Montana but previously I was using a larger WinCE device (in a case) and that would fill that space pretty well.