re: :) I didnt mean to be so abrupt
And in any case, the emitter is not a point object either.
In principle, the size of the shield at any point between Earth and the GRB is given by the conic section connecting the circumference of the Earth to the circumference of the GRB - a very long , slightly tapered soda straw through space. Since the GRB emitter is likely to be a planet-sized black hole, at least, you will never get away with a coffee lid...