Issues with pole reduction map

Hello! I’m having an issue with my code:

gmt grdredpol w3m.grd -R-91/-65/-17/-5 -Grtp.grd -W2 -V

for reducing the magnetic anomaly map pole that is in the GMT database, and I can’t seem to get it to calculate for the entire grid. I appreciate it in advance if someone could help me. Here are the resulting figures with -W2.

The RTP operators are very unstable at low latitudes. Sorry but anything below ± ~10 degrees (or more) are not usable for RTP’s.