Normally, unless you're using the thin wall installation (i.e., say a fiberglass one-piece), there's no reason to keep the thing in place after you've got it positioned properly (well, it will help keep thinset, etc. out of the trim mounting holes, so you could leave it a bit longer). I HIGHLY recommend you temporarily install the trim and then get the valve set at a depth YOU like. If it's installed between the min/max marks, the trim will fit, but YOU may not like the way it looks. To the manufacturer, if it fits, it's okay, but that isn't necessarily what you want...mock it up first!