Scaling object at runtime based on orientation

Hey guys. I have a system that checks if the player’s cursor is within a set of runtime-created, constantly-scaling bounds. In this system, I want to scale only the square-base and not the height. However, whilst setting my prefabs up, I cannot reliably guarantee that each GameObject has its x and z dimension always laying on the ground, especially if there is alternate rotation applied during runtime. I was wondering if I could somehow get the dimension that faces upwards (essentially the vertical height), so I can scale the other two dimensions. Any assistance or alternate solutions are much appreciated!