Directional Wifi Antenna
I would consider a patch antenna. With a thick enough substrate you can cover the entire Wi-Fi 2.4 GHz band. It has a pretty decent front to back ratio (>10 dB) and an almost onmi hemispherical pattern. 

While it is impossible to say for sure from you description, it doesn't sound like the antenna is the problem. If it were, you would have had a lot more problems in Tx than Rx (Tx is usually at least 50 dB above Rx). The fact that you are having problems in Rx makes me suspect some sort of coupling between your LNA and analog circuitry. When you put absorbers, you are lowering the signal level in the LNA (or further down the receive chain) and decrease the coupling.