You are incorrect, sir. In 2010, it could be mounted in any of the corners of your windshield, but in 2017, they reduced it to only the lower corners of your windshield. HOWEVER, Uber/Lyft drivers are in violation of this CVC with their signs, especially if they are working for both. Just a matter of time before one of the CHP officers, sheriffs, or local PD starts cracking down in them.
https://legalbeagle.com/6513133-california-gps-windshield-law.html
https://www.rammount.com/blog/2017/01/california-hands-free-law/