Dependent Dropdowns- reference sheet

Hi. I am trying to create an app that has 4 dependent dropdowns - but I also have other columns in that sheet for the user to input data. Should I put the dependant on a second sheet and than reference the second sheet? How do i get app sheet to recognize the second sheet as a reference, I have tried valid if but doesnt seem to pick up the reference?


Please see the support doc for Dependent Dropdowns:

And this post regarding expression for Valid_If: