Constraining a dimension in a component

Laggingbehind

Hi, Basically I need to create a dynamic component of this worktop where the length & depth will change.. I'm happy with how to do this but the bit I'm struggling with is when I need to change the depth of the worktop shown at 650mm I still want the upstand depth to remain at 20mm....currently if I want it say 700mm the upstand dimension also scales up too. The worktop on the left just shows what the back looks like for reference.

JQL

The simplest way is to separate it in two pieces. The upstand must be a component with fixed depth and the worktop must have a fixed location attached to the upstand and a free depth.

They can be either groups or comps and must be nested in a global component wich has variable depth.