How to call GetTapeParameters?

I am trying to use GetTapeParameters to get the media parameters.  When I use the code segment below, I get a MORE_DATA error with 32 returned in tape_parms_size.  The size of tape_parms is 25.  If I change the tape_parms type to TAPE_GET_DRIVE_PARAMETERS which is 32
bytes then the call will work.  However,  if I don't use the
TAPE_GET_MEDIA_PARAMETERS type then I don't know which bytes represent the block size.  Why is the GET_TAPE_MEDIA_INFORMATION call returning
a structure that is larger than TAPE_GET_MEDIA_PARAMETERS and how do I
know the layout for the structure that it is returning?  I am using Windows NT 4.0 with an Exabyte EXB-8505 8mm tape drive connected to an Adaptec  AHA-2940AU SCSI controller.

TAPE_GET_MEDIA_PARAMETERS tape_parms;
DWORD tape_parms_size;

status = GetTapeParameters(hTape, GET_TAPE_MEDIA_INFORMATION,
&tape_parms_size, &tape_parms);