检测SKSpriteNode何时完全低于另一个SKSpriteNode

For a game I'm creating, an SKSpriteNode gradually makes its way down the user's screen. There's another SKSpriteNode (position is static) near the bottom of the screen, leaving only a little bit of space for the original SKSpriteNode to fit in. I need to detect when the first SKSpriteNode is COMPLETELY below the second SKSpriteNode, which I'm having a bit of trouble with. Here's the code I'm currently using:For a game I'm creating, an SKSpriteNode gradua