I spoke to a BMW tech at a bike show and asked why they went with the booble head design. He told me it was because the parallel twin creates a vibration at "x"rpm that caused the brake fluid in the front res to aerate and it was causing issue with the ABS system. It was only at a very specific RPM but they decided better safe than sorry and rubber mounted the res to resolve the issue.
Camel Tank auxiliary fuel tank for F series BMW twins. www.Camel-ADV.com