Some aerials need a ground plain, That is normally the steel roof. The kit shown i believe is the basis for shared DAB, FM. The T6 has all its Antenii shared between two door mirrors. That is FM, DAB, GPS, Mobile phone. It is of convenience and profit to the Dealers only constant breakages and poor reception compared to roof mount. The T6.1 has a nob head rubber sheath on the front roof containing what ever aerials where ordered from new. There are VAG type retrofit dealer around GB that might do a shark fin with as many of those aerials as you wish. certainly the one in Poole Dorset sells and fits them usually on the rear roof. At least that is where they said they would put mine probably because it is a Caravelle with all sorts of other stuff in the way in the front roof.
I thought that your vehicle was a 6.1 with the rubber boot front roof? Have a look at the Poole website see what they have and communicate with them they may give some advice or even fit it for you if yo wish.
Specializing in Supply & Installation of Audi & Volkswagen Retrofits throughout the UK. Using all Genuine Parts and a Bespoke Nationwide Installation Service.
www.advanced-incar.co.uk
www.advanced-incar.co.uk
www.advanced-incar.co.uk