There are lots of factors as to why it isn't working the way you think it should. In a perfect world, with no air, obstructions, and perfect antenna, an omni directional antenna's radiation pattern will look like a doughnut with the antenna going through the hole. The higher the db the flatter that doughnut will get, but the farther it will reach horizontally. Since we don't live in a perfect world, and there's shit all around our antennas, the doughnut will look more like something a kinder-gardener would make. It's going to have bumps and odd lumps around the pattern. It could also be tilted one way or another, so when you think it should be straight, after all the antenna is pointing straight up, it's tilted. I've seen antennas so screwed up that if you walk out past 20 feet or so your signal will drop almost in half, but only if you walk one direction, go the other way and it stays fine. It also depends on how the antenna is attached to the radio. Is it directly connected or is it using a cable? If it's a cable, what's the loss of the cable? Are there any kinks in the cable, cause that will cause additional signal loss over the normal signal loss of the cable. Was the little Malaysian kid that made the cable having a bad day? Maybe he didn't get the connector crimped quite right.