I am seeing the FIS-B data as well. I don't have a Mode S transponder so all traffic is coming from the NavWorx box. I do not remember what the MAXDIST and MAXALT parameters are set to.
What seems to happen is when I take off from FCM I get traffic almost immediately upon climbing. It disappears somewhere 20-30 NM from MSP. Upon coming back to the MSP area, I often don't get traffic until I am a lot closer to MSP than I was when it originally stopped - sometimes almost on top of FCM. I think I am getting FIS-B information before I see any traffic.

I've never seen traffic displayed anywhere other than what I described above, and so far the max I have seen is 16 targets.

I am going to recheck my cable from the NavWorx box to the antenna. It's possible there's a problem, such as a short, causing it to attenuate the signal and hence dramatically reducing the range. I do know that I enabled the transmitter, so that's not the problem.

I've also seen another graph somewhere showing the location of ADS-B ground stations. It only shows 2 of them in MN, one at MSP and another to the southwest (perhaps MKT?). It sure doesn't look like the state has a lot of coverage at present. The FAA ADS-B site only shows what the coverage is projected to be by 2013, so that information isn't terribly useful. So I am confused about what the ADS-B coverage in MN really is at present.

Mark Olson F1-EVO