I don't believe that the sort of loss you are seeing is that surprising. The RF signals drop off really quickly close to the antenna. In the first 2 meters (@ 5.1GHz) you'll see loss of abut 52dB, extending this out to 4 meters and the loss is only 58dB. Think of a circle one centimetre away from the antenna, and consider its circumference. Now consider the circumference of a circle two meters away from the antenna - there is a huge difference.
The power transmitted from the antenna is distributed roughly evenly around that circumference at 1cm radius, and the same power is distributed roughly evenly around the circumference at 2m radius. The circumferences are 0.062m and 12.56m respectively - it is a huge difference.
Now some of the features we have in wireless access points, especially maximal radio combining (MRC), allow us to receive multiple signals and combine them to achieve a better overall signal, but ultimately the losses close to the wireless access point are huge.
I know I haven't really answered your question, but I hope it helps in understanding that the losses you are seeing are not really surprising (in fact I'd say only 70% is good).