Since upgrading to RAS v16.2, paper size which you selected locally at Print Preferences is not redirected to published application print preferences.
Please upgrade to v16.2.3 (19419) or newer
1. At Parallels Client got to Connection Properties > Printing tab > Options > select Use client preferences for all printers
2. Re-login to Farm and launch the application. A local printer preferences dialog will open when you click Print in an application. The dialog will contain a full set of options for a particular printer that you have installed on your local computer including paper size setting.