How to set a “default folder” to an Asset Picker

Question

I'm trying to create an asset picker which matches my needs. I have the asset picker in my Custom Field and i want it to open the dialog from the List he is in.

I wrote down this code:

            urlSelector = new AssetUrlSelector();
            urlSelector.PickerButtonText = "Add";
            urlSelector.AllowExternalUrls = true;

            //Get current list
            string app = this.Context.Request.Url.ToString();
            Match m = Regex.Match(app, @"/Lists/.*/");


            urlSelector.DisplayLookInSection = false;

            //Associate the right path
            urlSelector.DefaultOpenLocationUrl = "~Site" + m.Value;
            urlSelector.DefaultToLastUsedLocation = false;
            urlSelector.AutoPostBack = true;
            this.Controls.Add(urlSelector);

Am i doing something wrong?