As a test awhile back I tried the "coat hanger mod". Cut about a foot of straight wire out of the bottom section of a standard wire coat hanger. Then with black electrical tape, fasten the foot long coat hanger wire directly to the plastic antennae of the CM15A. I couldn't believe the difference this made in my X10 range, especially for remotes that didn't send a very strong signal to begin with. Now my stick-on wall switches and keychain remotes work as I initially expected them to.
Why the makers of X10 don't make this cheap mod before packaging is beyond me. It would make for many happier customers.