I'm going to disagree with the other posters. I've installed a good number of wireless computers and have noticed significant differences in reception vs. head location. I don't claim to be an electronics expert, but it looks to me like a clear line-of-sight helps. I own a couple of recumbents both of which "stretch" the advertised range of their wireless computers. (31" for my single recumbent, 33" for my tandem) In both cases, mounting the pick up on the side opposite the chain made the difference between working and not working.

My regular practice is to install the wheel magnet and sensor first. Then I spin the wheel and hold the head close to the sensor to be sure that I get a MPH reading. Finally I hold the head in various locations on the handlebar and stem to see where I continue to get a signal.