Aftermarket windshields (OEE) use a different process to adhere the mirror brackets to the glass. I find that their quality of adhesion and location is not as accurate as OEM parts. In fact, aftermarket distributors repeatedly drip glue on the glass below the bracket which may stain the black ceramic band on the interior side of the glass. When it comes to sensor components such as a rain sensors, the problem it not as rampant. But on a BMW windshield, a mirror bracket not correctly aligned may hinder the re-installation of the mirror's plastic cover assembly which hides the sensor and bracket.