As I said in that thread, I believe flying should change how positioning affects targeting.
Here are some examples of how it could work:
If I'm standing on the ground, I can aim a single-target projectile at the orc. If I shoot at the goblin, I'll probably hit the orc instead. Because the bat is flying above the orc and the goblin, I can shoot at it. I won't ever hit the goblin or the orc if I'm aiming at the bat.
If I'm flying, I can aim a single-target projectile at the orc, the goblin, or the bat.
If there were a Tengu or fire drake in the bat's spot, it could fire at me over the heads of the orc and the goblin. I could also fire at it.
On the ground, I can fire at the bat or the orc without being blocked by the other. Both can target me.
If I'm flying, the orc can't target me without risking hitting the bat, and the bat may block my shots at the orc.
If we want to add another wrinkle, let creatures of a certain size (Big? Huge?) fire over heads (and be fired at) as well. They would block/risk being hit by any projectiles, whether fired from air or ground.
Now summon butterflies only potentially blocks ranged attacks from flying creatures!