For comparing two hierarchical clusters, I have read the paper "A Method for Comparing Two Hierarchical Clusterings" (Fowlkes and Mallows, 1983), as advised in the following stack exchange question: How do you compare the "similarity" between two dendrograms (in R)?.
In the paper they discuss even clusters, to obtain Bk, however, they mention that it may not be possible to obtain even clusters in each matrix and suggest using Bkl, where k is the number of clusters in matrix 1 and l is the number of clusters in matrix 2. They have not discussed Bkl theory or application.
Is there a paper or discussion of such a metric for uneven clusters?