Simulink RF Blockset: How do I specify the frequencies (ωRF + ωLO) for a mixer within the configuration tab?

So I'm building a little project with the end goal of simulating and displaying the result of a simple radar.

This is it so far:

As you can see I have a 1GHz signal which then 'splits into two' and one has a frequency offset added to it of 0.8GHz. So Import after the offset has a carrier frequency of 1.8GHz. And the signal without the offset has an Import1 block with carrier frequency 1GHz. These look fine in their respective scopes, but after the mixer I get this output in the Real Passband Scope1:

And this in the spectrum analyzer:

Which to me looks wrong as I;m not entirely sure why the peaks are at 1 and -1 after the offset at mixing. So, I assumed I hadn't specified (ωRF + ωLO) correctly within the RFConfig box as this uses the fundamental frequencies 1GHz and 1.8GHz whilst ωRF + ωLO = 2.8GHz or ωRF - ωLO = 0.8GHz. However, when I try to specify these frequencies manually under the Fundamental tones in the RFConfig to [0.8 2.8] I can't run the simulation and when I try [0.8 1 1.8 2.8] I get a 'too many carriers' error.

Does anyone know if I'm specifying these correctly and if not how I can go about doing that? If not, any suggestions would be grand, particularly going about testing the signals within the RF system as I can only see these signals once they're no longer within the RF system.