I might try the cm15a macro route but unfortunately the cm15a doesn't have much better range
X10 put a decent antenna on the tm751. Why can't they put that in the cm15a and the sc1200?? I mean it would only cost an extra cent or two in Chinese manufacturing. I guess I gotta mod the cm15a and put the tm751's antenna on it.
I can't speak for the SC1200, but there are a number of modifications you can do to increase the RF reception range of the CM15A.
The simplest one (which I did on two CM15A's) is referred to as the "passive reflector" mod, and doesn't involve opening up the CM15A or voiding the warranty.
Simply take a straight piece of wire, about 18.5 inches long, and attach it alongside the CM15A's antenna, making the bottom of the wire even with the "elbow" at the bottom of the CM15A's antenna. Use some tape, plastic zip-ties, or some other non-metallic material to hold the two together.
That's it. You aren't making an electrical connection between the two, but the longer wire acts as a "helper," to reflect the RF signals to the CM15A's antenna. I was skeptical at first, but it worked great for me, and plenty of others here have had similar success.
There are more complicated mods, including replacing the CM15A's antenna with a longer antenna, extending the wire, or even putting on a connector and making your own external antenna. I suggest trying the simpler mod first.
As for the SC1200, I seem to remember reading here that someone did the same thing (placed an 18.5-inch wire parallel to the plane of the built-in antenna), and had better results.