The proper answer of your question is given in reference "Triplet correlation functions in the Lennard-Jones fluid: Tests against molecular dynamics simulations William J. McNeil and William G. MaddenA. D. J. Haymet, Stuart A. Rice Citation: The Journal of Chemical Physics 78, 388 (1983); doi: 10.1063/1.444514 and "Three-particle contribution to the configurational entropy of simple fluids" András Baranyai and Denis J. Evans Phys. Rev. A 42, 849 – Published 1 July 1990.
I do not think the gentlemen you mentioned have solved this problem in a rigorous manner especialy close to the border of degenerate triangles.I and my colleagues have
pioneered the application of triplett correlations for biomolecules in water and electrolytes but I am still not satisfied with the methods we use which are OK for fat tripletts but problematic for quasi linear arrangements.