While the ant+ spec says it is capable of 100ft range, there is no requirement that all devices reach that range. Rather, sensor makers have your best interest at heart by only reaching a very near-field range (like from your bike-mounted power sensor to your handlebars), thereby reducing power and vastly improving the sensor's internal battery life. The Kickr operates from your wall power and can afford to blast ant+ signals at full power. Likewise, we can run the receiver at your pc at full power. So don't be surprised if you can easily receive signals from your kickr, but your bike mounted sensors drop-out first as you postion your bike further from the receiver at your pc.
receiver placement and using USB cable extensions
Place your USB stick where you can see it. Don't plug it into the back of your pc if that side isn't facing you. A front panel port is preferred. It's really easy to block signals. If you need to use a short (2ft) cable to get your stick to be in-sight of all stations, do that, but avoid long usb cable extensions. The reason is that most ports can't supply clean power over such long hops, and your receiver stick operation will be flaky. Laptops are notorius for being stingy with supply current here.
If you have a place that needs the USB stick to say, hang above all stations so that all device signals can be received (and this is a great idea), add in a powered usb hub at the far end (non-pc connected side) of the USB extension cable, and of course, connect the power supply to your ac power. Plug in your ant+ stick into one of the hub ports. This will ensure your ant+ receiver stick is mostly happy with its power.
We've also had great luck with "active usb extension cables". Basically these are cables with an integrated one-port hub, that powers from your USB port. The hub has some signal conditioning to match the cable characteristics and reduce data errors that are often seen on passive cables. So they are like the above diagram without the extra power supply. We use ours connected to a USB 3.0 port (higher power drive) even though it is a USB 2 cable and the ANT+ sticks so far are all USB 2 standard. Here's a link to an example.
Ant+ devices don't interfere with one another due to the channel coding, modulation scheme, and very clever time-domain signal spacing. But bluetooth, your wireless home-phone extension, your mobile phone's wifi, and even your home Wifi share the very crowded unlicensed 2.4GHz consumer band. All of these signals appear as noise to ant+ and can cause data errors and really affect range. If you think the data you see is a bit wingy, look around for emitting devices (including a microwave oven). You may want to move your Wifi to a new band, like 5GHz. That way every Wifi device in the room will page in on that band (if they are half-way modern).
We've also seen a curious USB3 hub really wreck havoc with our ant+ sticks. Basically a massive 10-port USB3 hub connected beside a USB3 port to which our stick was inserted. If you see something like really bad ant+ reception, look around for that sort of thing, and try to unplug the other device. If ant+ reception improves, you've found the source of the interference. Tell us about it!
ErgVideo controls your Kickr while you ride. You can have your garmin connected as well to receive data from your devices, but don't be sending calibration commands to your power meters or any sort of power-commands or calibration commands to the kickr. Basically, there is no way to "lock" who the kickr is listening to. It will respond to whomever knows its number, so to speak. So you can really mess up the session if you let another app run (for example, the kickr app on your ipad while riding ErgVideo...yeah turn that off!) while ErgVideo is assuming control. If you find the kickr to be doing unexpected things, look around the studio for someone connecting via bluetooth to kickrs and devices. It's probably the guy/gal paying most attention to their phone!