[WithinReason]

An explanation I read somewhere is that the radio waves reflect from the inside of your skull, the curvature acts as a parabolic antenna.

[eps]

That's a pretty dumb explanation if you pardon the bluntness. The effects shows itself regardless of how the head is turned reltive to the target.

[willis936]

Given the conductance of flesh and the frequencies at question the skin depth would only be a few cm at most. The RF energy never makes it through the brain.