Your math seems correct, but you're making some assumptions that might not work out in practice. First, the Friis transmission equation assumes that the transmitting and receiving antennas are in each others' far fields, but the 10 cm distance you specify is less than a wavelength (12.2 cm at a typical WiFi frequency of 2.45 GHz), which puts you in the "transition zone" between the near field and the far field, which means that your path loss may be different.
Second, your antenna gain of 0 dB basically assumes that your antennas are isotropic, which means that they radiate and receive equally in all directions. There is no such thing as an isotropic antenna in the real world, although there are real antennas that have 0 dB gain in specific directions. A "lossless" dipole antenna (another antenna that doesn't exist) has a gain of about 2.15 dB. So if you were using two dipoles in free space that were broadside to each other, far enough that they are in each others' far fields, then you would have antenna gain of about 4.3 dB.
So it's not possible to give an exact estimate of the gain you would see in real life from the information that you have given us. I'm not an electrical engineer, but I think that you would have better coupling (more gain) than your calculations say.
