The field enhancement factor at the emitter tip and its variation in a close neighbourhood determines the emitter current in a Fowler–Nordheim like formulation. For an axially symmetric emitter with a smooth tip, it is shown that the variation can be accounted by a cos θ factor in appropriately defined normalized co-ordinates. This is shown analytically for a hemiellipsoidal emitter and confirmed numerically for other emitter shapes with locally quadratic tips.