The structure spawn x and z offsets are not working for me.

I've been trying to make a custom tree that spawns in my dimension. I'm generating it as a structure so that it can be completely custom. The Y offset setting is working correctly, but the structure "center point" is at one corner. Since the tree has a base of one block at the middle, and the center point is in air, the tree can spawn floating because the center point is on land but the base of the actual trunk is offset by a few blocks, often over a ledge. I've tried to edit the x and z offset settings to center it on the trunk, but the center point never actually changes no matter what numbers I set them to. Help!