Just finished an in-depth study of this. It turns out that my picture above is best interpreted by taking the center of Link's position, which would shift my squares down and right by 8 pixels each. From that, you can see that the safe zones are centered on the mouths of the statues (which are in different places for the two types) and extend 24 pixels in each direction, for a 48x48 (or 49x49, not certain there) pixel safe zone for each.
Just wanted to put it down for future reference.
EDIT: A related note: The NES aiming of the fireballs is not as accurate as ZC's, which means there are places you can stand (outside the safe zones) where a statue will fire at you all day and never hit you. Not sure on the algorithm yet.
EDIT 2: By making a visible shooter enemy, I have discovered that the spawned shooter enemies are not centered on the statues, but rather on the mouths of them. So, this becomes even easier to fix. As the Shooter enemy is offset from the statue, in the same way is the safe zone. If Link's sprite is anywhere within 16 pixels (one tile) of the shooter enemy, then it will not fire (on the NES).
IOW, if the center point of Link falls inside any of the 48x48 pixel zone which is centered on the shooter enemy, it won't fire. Think of it as a hitbox that is larger than the "monster", and causes no damage if touched.
