Voodoo / Sox
Yes, the EC offering for TCAS I has only one directional aerial on a very small ground plane, and bearing accuracy / detection is poor as a result. The Bristow offering for TCAS II has directional aerials above and below the fuselage with massive groundplanes, so the bearing accuracy and detection is very good, however its big and heavy.
As Buddah says, the middle path is the best way, with a compromise between the two extremes above!
HC