Yes you must mount a largest nozzle. I ordered a 0.8 nozzle to that : the result is amazing and with transparent filament is better.
On my Reprap printer (like prusa MK3) I have a 1mm nozzle to this effect.
With 0.4 nozzle, you can have a width of 0.44 or 0.48. You can try other preset to increase a little bit the width in the slicer