
I got a sample from someone where one parent was a West Bengal Sadgop, and another parent a Baidya with family origins in East Bengal. One hypothesis that I’ve see is that Baidya are basically Brahmins who lost their caste. Genetically this does not seem to be the case. Bengali Brahmins shift considerably toward the steppe samples compared to average Bangladeshis, and this individual does not. Rather, their uniqueness is that they have very little East Asian ancestry compared to the median. This is typical of non-Bramin West Bengalis. It is plausible to me that this individual’s Baidya parent, from East Bengal (Bangal), had more East Asian ancestry than their West Bengali (Ghoti) parent, so you see an average.
Though there are some exceptions, it seems that the non-Brahmnin bhadralok castes did undergo ritual uplift from that of conventional peasant cultivators at some point in Bengal. This seems similar with regard to Kayasthas in UP, but not in Maharashtra, where CKPs seem to have an affinity with Brahmins distinct from the Maratha cultivators.
Update: I found a preprint that pretty much answers all the questions re: Bengalis.
Here is a panel with a UMAP representation of genetic distance, and you see West Bengal is adjacent to Bangladesh. But there is a “tail” of individuals that are parallel to South Indians.

This UMAP makes clear Bengali Brahmins are distinct from Kayasthas and Sadgop. These populations seem roughly similar to most Bangladeshis except they are shift over, and I assume this means less East Asian ancestry, as PCA seems to how:
