hard to think about an antenna from a hot ceramic but I get it now kinda, so as you change size maximum thermal emission changes which is why things don't make disproportionate amounts of energy in limited bands, but with small particles the emission should be greater because they are small, but overall less because the medium is less dense, and the definition of blackbody requires some particular grouping, and you get radiation transfer between them rather then conduction since they are a bunch of free particles so its kind ablocking itself?
I kind of gather that it has to do with general density, because there are reflections in the medium and stuff between the atoms (seems really complicated if you get into it), let me see if i can find the web page that got into this,
https://www.quora.com/Why-does-a-gas-discharged-under-low-pressure-give-non-continuous-spectra-whereas-it-gives-continuous-spectra-under-high-pressure"
However, as you increase the pressure of a gas, the atoms start bumping into one another more frequently. If two atoms collide while an electron in one of them is in the middle of emitting a photon, the emission process is cut short and the lifetime δt
is reduced. Consequently, due to the uncertainty relation above, the spread of frequencies δf of the emitted photons increases. This phenomenon is called pressure broadening of spectral lines. If the pressure is high enough, and the collisions are sufficiently frequent, the bands in the above picture start to blend into one another and you go from a discrete spectrum to a continuous one:"
I think that especially with complicated molecules things can get really funny here based on how that mechanism works.