My keyless entry range is ridiculously poor, usually about 18" from the body. In addition, the remote only functions when held in certain locations around the body. I've read and heard the stories about interference, but that's a poor excuse. Can this be remedied? Is it common?

I have the exact problem. If you find that you have better distance after replacing the battery, give us an update.

I have a range of about 25 ft. with both of mine. You didn't say if you have tried a new battery and this sounds like it could be low. If you tried one already, then verify that it has the correct battery. It should be a 3 volt. If that's not the problem, then I believe you have a defective remote.

I replaced the battery in each of my two fobs. One works better than the other. Overall there was some improvement, perhaps 10%, but performance is still well below what I see on other vehicles. I don't think it's the transmitter, I think it's the receiver or the antenna.

This is a fun hint;
If you direct the remote key to your head (the temporal lobe area) you will trippel the reach.
I have normally 25 - 30 feet (app. 10 meters); when using my head I have succeeded to have a 75 - 80 feet reach (app. 25 - 30 meters).