[Paragrouper]

I'm not sure what the topic is where you will post, but you make some critical points about gain versus directivity that cannot be stressed enough when evaluating an antennas performance, especially when the antenna data is provided by a manufacturer (full disclosure; I work for one).
Antenna gain is primarily impacted by directivity across a stated frequency range. It is often expressed in a manner that can be misleading. When evaluating the stated performance it is important to understand the application that the antenna would be used for—more gain is not always better. A common example, a high-gain antenna used to point at a satellite from a fixed point on the ground would not be suitable for use on a vehicle that is traversing over uneven terrain, where you would want a more hemispherical radiation pattern to support communications on the move. A lot of the vehicular TACSAT antennas (crossed dipoles, a.k.a. X-blades) on the market provide you with ~5-6 dBic (or more) gain, measured at zenith, which is a respectable value. What this means in practical terms is that if you have a high look angle to the satellite, the antenna works okay. However, once your look angle falls below 35-40 degrees you will lose link. Those who have used these types of antennas in areas with low look angles to the satellite or in extremely uneven terrain will know what I’m talking about. If the gain is stated higher than 6dBic the problem will be worse. Other designs, such as helix antennas, will provide a more hemispherical pattern even though the stated gain is usually less than 3dBic.