I'm trying to find out how range decreases within 10 meters.

I think path loss can help me. Here is my calculation,

PATH LOSS(dB) = 32.44 + 20*log(F(MHz)) + 20*log(D(km)) - Gtx(dBi) - Grx(dBi)
PATH LOSS(dB) = 32.44 + 20*log(2400) + 20*log(0.0.1) - 4 - -1.4
This equals to -65.4dB

Based on Cisco Aironet 2700. I thought I need to compare this value with the Receive Sensitivity @ -90 dBm for 802.11b, 11Mbps. Although this is in dBm so surely I can't compare the two values.
What value am I looking for on an Access Point?

Then with the results I believe "for every decrease of 9dB, the indoor coverage area should be cut in half".