I'm just wondering if anyone knows of a way that you can link a dimensional equation to a dimension in a sketch that is dependent upon say the thickness of a Boss-Extrusion?

For instance I have a plate that I extruded that is .75" thick. Now I want to put a slot in the end of that plate but I want the slot to always be 1/3 the distance from the bottom surface of the plate even when I change the thickness of the plate. Can this be done?

Thank you for any thought/expertise...