To get a "qualitative" feel for the effect of the tailwind - you can think of it as "my pellet will encounter as much air resistance as it would if it the muzzle velocity was reduced by the wind velocity". (since the velocity of the pellet is less relative to the air). This means less air resistance, hence more retained muzzle velocity throughout the flight, hence, slightly higher POI. Exactly how much, ballistic calculator will tell you.