Graviman - Omigod. Is that a myth ? I thought that was true, at least for long grass.
Letsby Avenue (Great name ! Almost as good as Paul McKeksdown) - In fairness to Delta3 I think the formulae were for my benefit rather than the students. I don't mind simplifying things but the idea of a pressure bubble 'supporting' the helicopter seems a bridge too far to me. It's not supporting the helicopter - it's making the rotor more efficient.
For the PPL they have to know about induced drag, how autorotation works etc. so there's no avoiding some basic exposure to vector diagrams, and no great additional complexity to show them how those diagrams change when in ground effect.