Radius-Based Hit Detection

Enemy.cs

public class Enemy : Sprite
{
    public int HitRadius { get { return 10; } }
}

Projectile.cs

public class Projectile : Sprite
{
    public override void Update(GameTime gameTime)
    {
        foreach (var enemy in EnemyManager.Enemies)
        {
            var distanceToEnemy = Position.DistanceTo(enemy.Position);
            
            if (distanceToEnemy <= enemy.HitRadius)
            {
                // Hit!
            }
        }
    }
}