The antennas on these things really suck. In fact, so far, all the antennas in every X10 device that I've bought (over $1000 - fool me!) don't have any real reach.
I started on this X10 stuff just about a month ago, and let me tell you, had I known what I know now, I would have never done it. I dove right in and bought all kinds of stuff (cameras, video sender/receiver, remote controls, LOLA, full house alarm, AHP, filters, repeaters, powerhorns, etc.) Now, I'm in debug mode - for just about everything I purchased - what a waste of time! Don't get me wrong, at first the idea of learning, digging, and playing with something new to me sounded great - little did I know.
Anyway, if the antenna on the CM15A is any indication on the "quality" of the antenna inside the case for the sender/receiver, I doubt you'd be able to get it two floors up. I tried and failed miserably - no matter what direction I pointed the sender & receiver's antennas to. Your best bet is to point both of them to the ceiling, play around with the channels, and hope to get something. Otherwise, you'll probably need a 2.4ghz signal repeater. Also, if you have a wi-fi network, be careful. These devices do interfere with it.
What's worse is if you have other X10 devices that use RF, even though they use a different frequency, they caused problems for me. The claim is 100ft reach for the sender/receiver, but that's actually if you have them in TOTALLY open space with no interference whatsoever (not even the wind).. Try to create that scenario in real life!
Keep in mind that if you do get them to work, anyone with a strong 2.4ghz video receiver (like the ones used for babycams) will be able to "share" what you're viewing on your TV. If that happens, it will definitely steal badwidth too.
My recommendation would be to find a way to replace the antenna in both the sender & receiver. It will probably void your warranty though. That's what I had to do with my home automation USB unit (CM15A). It came with about a 5 inch piece of wire as the antenna (enclosed in a small plastic tube for professional presentation)! PLEASE! I replaced it with a UHF/VHF (rabbit ear style) antenna and now, my reach is much better.
Frank