seems regional. i use tang for all cousins on my father's side, without exceptions.
the cousin differentiation is probably one of the more meaningless differentiations anyway - when addressing our cousins directly or within the family, we simply address them by ge or jie if they are our seniors, and directly by name if they are our juniors.
It’s not father’s side or mother’s side.
Tang 堂 is fathers brothers children. Every other cousin is 表 biao.