The bulk update request #11449 is pending approval.
create alias sitting_on (436) -> sitting (348370)
create alias standing_on (47) -> standing (487792)
Reason: I figured it's better to just make a BUR now than keep the separate discussion thread going. I've hidden the other topic to consolidate all feedback in one place (only Rainbow Dash replied suggesting the alias route).
The wiki entry for sitting_on states that it's for "sitting on something or someone", but the inclusion of "something" means that it could mean sitting on anything and is thus functionally synonymous with just sitting. We already have the tag sitting_on_another for the purpose of sitting on another living being or animate inanimate. If a character is sitting on an object that doesn't have an existing sitting_on_* tag, then it should just be tagged sitting with the object tagged separately.
By contrast, standing_on seems intended to be used for standing_on_another. However, the tag is still ambiguous since a user who hasn't read the wiki may assume it means standing on anything, and it's safer to alias it to the general term standing to avoid mistags over potential missed tags.