VARYING, options(*varsize) and exit point programs

At the following registration point:
                      Exit 
Exit                  Point 
Point                 Format    Registered  Text 
QIBM_QTMF_SVR_LOGON   TCPL0200     *YES     FTP Server Logon

I have the following code, (shown below).

However, the variable USRIN seems to contain the values for several of the 
other variables.  These other variables not only appear in USRIN, but also 
appear in their respective variables.
Am I doing something wrong, or am I forced into doing something like:
 USRIN=%substr(usrin:1:usrlenin);

     D FTPLOGONN       PR      *entry plist
      * Input parameters:
     D  x01                                like(appidin)      Application 
ID
      *                                                    possible 
values:   1 = FTP Server Program
     D  x02                                like(usrin) options(*varsize)  
User ID
     D  x03                                like(usrlenin)      Length of 
User ID
     D  x04                                like(autin) options(*varsize)  
Authentication Strg
     D  x05                                like(autlenin)      Length of 
Auth. Strg
     D  x06                                like(ipaddrin) 
options(*varsize)     Client IP Address
     D  x07                                like(iplenin)      Length of IP 
Address
      * Return parameters:
     D  x08                                like(retcdout)      Return Code 
(Out)
      *                                                    possible 
values:   0 = Reject Logon
      *    1 = Continue Logon
      *    2 = Continue Logon,
      *        override user pro-
      *        file and password
      *    3 = Continue Logon,
      *        override user prf
     D  x09                                like(usrprfout)      User 
Profile (Out)
     D  x10                                like(passwdout)      Password 
(Out)
     D  x11                                like(CurLibOut)      Current 
Lib. (Out)
     D  x12                                like(CurDirOut) 
options(*varsize)    Current Dir. (Out)
     D  x13                                like(CurDirOutLen)      Len of 
cur directory
     D  x14                                like(AppSpecDta)  Application 
specific
      *       data (Out)
     D  x15                                like(AppSpecDtaLen)      Length 
of applica-
      *       tion specific data

      *
      * Define parameter list
      *
     D FTPLOGONN       PI      *entry plist
      * Input parameters:
     D  APPIDIN                      10i 0      Application ID
      *                                                    possible 
values:   1 = FTP Server Program
     D  USRIN                       999a   varying options(*varsize)  User 
ID
     D  USRLENIN                     10i 0      Length of User ID
     D  AUTIN                       999a   varying options(*varsize)  
Authentication Strg
     D  AUTLENIN                     10i 0      Length of Auth. Strg
     D  IPADDRIN                     30a   varying options(*varsize)  
Client IP Address
     D  IPLENIN                      10i 0      Length of IP Address
      * Return parameters:
     D  RETCDOUT                     10i 0      Return Code (Out)
      *                                                    possible 
values:   0 = Reject Logon
      *    1 = Continue Logon
      *    2 = Continue Logon,
      *        override user pro-
      *        file and password
      *    3 = Continue Logon,
      *        override user prf
     D  USRPRFOUT                    10a      User Profile (Out)
     D  PASSWDOUT                    10a      Password (Out)
     D  CURLIBOUT                    10a      Current Lib. (Out)
     D  CurDirOut                   100a   varying options(*varsize)  
Current Dir. (Out)
     D  CurDirOutLen                 10i 0      Len of cur directory
     D  AppSpecDta                         like(AppSpecDtaDS)  Application 
specific
      *       data (Out)
     D  AppSpecDtaLen                10i 0      Length of applica-
      *       tion specific data

Rob Berendt
-- 
"They that can give up essential liberty to obtain a little temporary 
safety deserve neither liberty nor safety." 
Benjamin Franklin