GeometryReader not generating correct screen height?

  public var body: some View
  {
    ZStack{
     
      GeometryReader { geometry in
          RoundedRectangle(cornerRadius: 25, style: .continuous)
            .frame(width: geometry.size.width*1.00, height: geometry.size.height*1.00)
            .zIndex(0)
      }
  }
}

I'm using GeometryReader to draw a rounded rectangle to fill up the entire watch screen, this looks fine on a 38mm watch simulator, but as I increase the watch size to 40, 42, 44mm I noticed that the height is not filling up the whole screen. I have to adjust my multiple to say 1.1 for example to fill up more of the screen.

Can someone tell me if I am using GeometryReader incorrectly?