A 20-foot tall eucalyptus could easily host mycorrhizal fungi 40 feet away IMO. Sounds like your eucalyptus are quite a bit larger. I know of only 3-4 Eucalyptus species which can survive our winters here for over 5 years: one of the reasons Sequoia sempirvirens doesn’t do well long-term here either.
The close-ups in photos 2 & 3 look to be of the upper right sporocarp of photo 1. Is that correct? The cross-hatching visible on the outside of the gills clearly suggests to me formation of loculate-like chambers. Hypogeous growing under humus layer also supports that formation. Your observation specimens seem quite a bit larger than anything I’ve seen locally. I’d guess some of them are 3-4 inches across? The interesting thing to me is that individual sporocarps have varying degrees of gill fusion and spore sequestration. This further supports IMO the Macowanites identification.
If you find any within stipes, that would be an additional feature towards Macowanites in my sense of the genus. A lot of the species identified by Gilkey and collected from Cape Lookout S.P. have very short, barely noticeable stipes. While my collections there have largely been mere footnotes, the collections over time seem to support Gilkey’s evolutionary schematic of Russula mushrooms becoming more and more hypogeous over time.