Why are the parameters in the custom code in my tool working but not the ones I set in the tool UI?

If you set parameters globally in the custom code in your Target tool settings (like the below for example), then this will override any parameters you set in the tool UI since they're leveraging the same function. You can set parameters in the custom code in the tool if this is your preference, but you will be limited to this method since the UI fields will not be effective.