Okay, in this scenario, please try...
Make the STM object the child of a layout group.(Horizontal Layout Group, Vertical Layout Group) and set the layout group to have "upper right" child alignment, and uncheck "child focre expand" width and height.
Next, remove the content size fitter component from the STM object, and it should follow the rules of what you want. (Within the bounds of the layout group) Unity Layout stuff works a bit strangely, so apologies for all this. It's a bit weird to set it all up.