@Cam_Boi_Doi It's a property of a structure called "CrushDepth" (+ possible bonuses from upgrades). It can only be edited in xml, not in any of the editors.
@Cam_Boi_Doi It's a property of the structure (not defined in the vanilla structures, which makes it default to 3500). I.e. you need to add crushdepth="xxxx" to the structure config.