An SKSpriteNode not following another node properly

Question

In my game scene I have a ball, a magnet and a platform called leveUnit as seen below

 import SpriteKit
 import GameplayKit

class GameScene: SKScene {

var ball = SKShapeNode()
var magnet = SKShapeNode()
let worldNode:SKNode = SKNode()

var levelUnit = SKSpriteNode()

override func didMove(to view: SKView) {

    ball = SKShapeNode(circleOfRadius: 30)
    ball.fillColor = .yellow
    ball.position = CGPoint(x: 0, y: 200)

    magnet = SKShapeNode(circleOfRadius: 30)
    magnet.fillColor = .blue
    magnet.position = CGPoint(x: 0, y: 0)

    levelUnit = SKSpriteNode(imageNamed: "Wall")
    levelUnit.position = CGPoint(x: 0, y: 250)
    worldNode.addChild(levelUnit)

    self.anchorPoint = CGPoint(x: 0.5, y: 0.5)
    addChild(worldNode)

    worldNode.addChild(magnet)

    //addChild(ball)
    levelUnit.addChild(ball)

}

override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {

    let touch: UITouch = touches.first!
    let location: CGPoint = touch.location(in: self)
    let node: SKNode = self.atPoint(location)

    if node == self {

        magnet.position = location

    }
}

override func update(_ currentTime: TimeInterval) {
    // Called before each frame is rendered

    let playerLocation:CGPoint = self.convert(magnet.position, from: worldNode)

        let location = playerLocation
        let nodeSpeed:CGFloat = 20.5

        let node = ball

                //Aim
                let dx = location.x - (node.position.x)
                let dy = location.y - (node.position.y)
                let angle = atan2(dy, dx)

                node.zRotation = angle

                //Seek
                let vx = cos(angle) * nodeSpeed
                let vy = sin(angle) * nodeSpeed

                node.position.x += vx
                node.position.y += vy

        }
}

My problem here is when I add the ball to the levelUnit instead of just to the view itself it doesn't seem to follow the magnet to its exact position it just seems to hover slightly above its position while when I have it added to the view itself it goes to the magnets exact location. I am using the solution from this question here to make the ball go to the magnet's location.

what am I doing wrong? and what is causing this to happen?