Plot with psvelo outside of map boundaries

Hello! I would like to plot a legend for velocity arrows. I am using psvelo to plot the arrows on the plot, and then psvelo and pstext to plot the legend.

Plotting arrows on the plot:

psvelo file1 -R-10/10/45/90 -JR016c -A0.2sizec+a20+e+h0 -Se1c/1.0/2 -O -K >> psfile

Plotting legend:

psvelo -R-15/20/45/90  -JR016c  -A0.2sizec+a20+e+h0   -Se1c/1.0/2  -O -K << END >> psfile
15 55 1 0
pstext -Jx1 -R0/20/0/10 -O -V << END >> psfile
14.6 0.8 7.5 0.3 0 CM 1 mm/yr 

If I plot the legend as above using psvelo somewhere outside of the map lon/lat boundaries to not overlap with the map, nothing gets plotted even though -R option is expanded for that plotting line.
If I instead use a non geographical projection e.g. -Jx1, I can then plot anywhere in the plot, but the scale will not be completely accurate since the projections are different.

How can I plot the legend with psvelo outside the original map borders using the same projection as on the map?