Properly tuned arrow with a well-made broadhead = doesn't matter. I leave 1-1.5 inches (depending upon tune) of arrow beyond the back of the bow to protect my hand.
That written, I have to say with 2-blades I don't like the mental picture of a perfectly horizontal broadhead. I guess it reminds of the days back in the 70's when I didn't know about tuning and thought the broadhead brand, blade numbers, and orientation mattered. I remember missing a mule deer doe in Colorado (August 1977) by a body length as the arrow planed over the mountain.