Should not be included while measuring Entoloma spores, in this group in general it can make a big difference (as you noted).

I find it to be a very interesting species, I have been unable to photograph any examples of the basidia yet but will do more examinations soon and add more micrographs.

When making measurements of these spores is the length of the hilar appendage included in the overall length, the difference would be considerable as the appendage is quite large at 2.5µm.

A recent article by Co-David et al. in Persoonia (www.persoonia.org – free access) treats the phylogeny of the Entolomataceae, and also Richoniella, which is nested inside Entoloma (in the wide sense). The authors propose a new name for Richoniella pumila; the name Entoloma pumilum existed already.

Entoloma gasteromycetoides Co-David & Noordel.
Basionym. Richoniella pumila G. Cunn., New Zealand J. Sci. Technol., ser. B 22: 62B. 1940. Non Entoloma pumilum E. Horak (2008).

It is a gasteroid species belonging in the Entolomataceae, the pileus is in the form of a tuberiform gasterocarp and the gleba is loculate, the spores are cuboid with 4-5 sides and are typical of those found in other Entoloma species.
The stipe and columella are rarely observed so I was very happy to get nice images of the cross section showing both!
It is near the beginning of summer here and is at the end of the typical mushroom season, this is the first time I have found this mushroom and it was fruiting on clay soil amongst moss under tree ferns (Dicksonia squarrosa, Cyathea dealbata) and cabbage trees (Cordyline australis) near a small stream in native New Zealand bush!
I plan to add micrographs to this observation in the near future and will hopefully be able to tell if it is R. pumila f. bispora if I am able to view the basidia.

Do tell us more about it. What was it growing on/with? Have you found it at other times of the year, or is it seasonal? Is it typically epigeous as shown?