Setting DoShanghai = 1 instructs ClassAct to open the requester on a particular screen, designates the host-application screen as the current public screen, opens the requester, then resets the public screen to the default. This limits the time during which other windows could inadvertantly be diverted to the application screen.
Setting ChangePubScreen = 1 instructs ClassAct to open the requester on a particular screen, designates the host-application screen as the current public screen, opens the requester, but does not reset the public screen to the default. This maximizes the time during which other windows could inadvertantly be diverted to the application screen, but also hopefully maximizes the possibility of the FWCalendar requestors opening on the host-application screen.
If possible, use DoShanghai; if this doesn't work, use ChangePubScreen. Setting both variables will result in the behavior of ChangePubScreen. If neither of these options work, try a commodity such as MCX and use the FrontPublicScreen function.