With Star Wars ships and vehicles, as with any fictional vehicle, the sizes are often made up and don't exactly match the scale of a human, even when they put in effort to get it right. In this case though, I think it's not a problem with the scale, but with the cockpit in the model kit. The seat is not supposed to be high enough to be visible outside the canopy. You can see in this blueprint that the pilot's head is supposed to be just above the lower frame of the canopy:
I would use this blueprint to rebuild the cockpit at the correct depth and possibly scratch build a new seat as well in order to fit a 1:18 figure.