Hello,
As far as I know, you cannot use waveport inside the model domain. This means, waveports should be applied to an external face of your geometry.
If you absolutely need a port inside your model, you can use lumped ports.
Otherwise, just reduce the size of your external box in order to make it on contact to the faces of your geometry where you intend to apply the ports and remove the radiation condition on these faces.
Hope I gave you useful suggestions!
Francesco