@Herbert.Poellner
I did not find any command-line parameters to control this behavior,
but since just recently the Webex-Client finally does remember it´s last Screen and Window-Size = it the Client was quit when in full-screen-mode on Sceen 2 it will re-launch on Screen 2 on full-screen-mode again. (Version 41.5.0.18911 on Windows 8.1 pro german)