The following WARNING may be produced when a CELLWIDTH is applied to the HEADER location in PROC REPORT:

   WARNING: Use of CELLWIDTH/OUTPUTWIDTH= in a spanning header or footer
   will rarely yield expected results. For conventional usage, specify
   outputwidth only for the data column cells.

Changing the location from HEADER to COLUMN will remove the WARNING.

In your program, you would change the following.

   style(header)=[cellwidth=n]

 to

   style(column)=[cellwidth=n]