The dot diacritic works for [dzo] to [jo] , for [do] to [ro] and for [dho] to [rho]. But /ba/ and /ra/ are completely unrelated sounds, so what is the dot doing to /ba/?
That “dot” symbol is called BENGALI SIGN NUKTA (U+09BC) in Unicode, and is used “for extending the alphabet to new letters”. Other Indic scripts also have nukta signs for the same purpose.
The following are examples of its use. The last three are precomposed characters in Unicode. I'm using Unicode names.
Base Letter With Nukta ক KA ক় QA ফ PHA ফ় FA গ GA গ় GHA জ JA জ় ZA ভ BHA ভ় VA ড DDA ড় RRA ঢ DDHA ঢ় RHA য YA য় YYA
However, র BENGALI LETTER RA doesn't appear in Unicode as precomposed with NUKTA, as RRA, RHA and YYA are. It could be that RA and ব BENGALI LETTER BA are independent letters.