Recently I've retrofitted cic with an ebay gps antenna. So, l've noticed something. Wherever I place the antenna, it shouldn't be below something. It doesn't matter if it's thin or thick. For example, if I place it at the corner of the A-pillar on the dash, it successfully receives the signal in few minutes. However if I fix it below the A-pillar trim, it doesn't work. No matter which antenna I use. So, I also tried it with other brand gps antennas. However in my other brand car, it succesfully works when I hide the antenna below A-pillar trim. I think it's not due to the antenna, but due to the gps receiver inside the cic or the material of the trim. As if Bmw has produced a trim just like a tank armor.
