The SFTON and SFTOF commands do not work with FWD and BWD/BACK, they only work with INTERLOCK + TEST START and PLAY. These commands allow you to do a temporary shift of the job in pulse, Base Frame, Robot Frame, Tool Frame or User Frame.
Your job should look something like this:
MOVJ
MOVJ
SFTON P020 RF
MOVL
MOVL
SFTOF
in this case, the MOVL's would be shifted the amount specified in P020 in Robot Frame.
Hope this helps!