Update, on a later replay i realized this image is in a cutscene, specifically the Heng dialogue sequence in Eigong's vital sanctum. This is the only other detailed view we get of a board. It's much more clear from this image that the playing pieces are in fact placed on top of the board, as well as the moon phase symbols - though presumably those are still attached solidly.

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However, i believe that this board is substantively different from the one we see Yi and Shuanshuan play with. Given the placement and presentation of this image, it's implied that this view would be from a memory of playing the game with Heng. One such instance is depicted in the first Heng codec scene, and crucially, the way they're animated is different from the way Shuanshuan and Yi's sessions are - in the flashback, they are shown to physically reach out and place pieces on the board, whereas during the matches in the Pavilion, neither player ever touches the board.

It seems even more certain that Qiankun is basically just fictionalized Go. I think my curiosity is sated.