The valves typically come with a plaster guard - a cover to keep things clean and help align the valve prior to installation of the finished wall coverings. Typically, there will be min/max lines on that cover for the depth. The guide also is the template of how big, where, and the shape of the hole that is needed in the wall. This is also usually discussed in the installation manual, which you can often find on their website. this varies and is specific for each company and each valve, so no generalizations are valid for an actual specific installation.