DB - I did my RAF pilot's course in 1983 and my QHI course in 1989 and taught on the Army Pilot's course whilst on exchange in the 90s and it was called a double angle approach in all three iterations
I cannot comment on which of the 3 causes you have suggested might be the one
If you remember quickstops finished at 30 ft in the hover on the Gazelle which is firmly inside the H-V curve (which of course wasn't a limitation in the RTS or ACM). Most of the military stuff on the APC (CAs, Obs and Recce etc) involved operating in the 'avoid curve' but, as we said earlier, there are many jobs that must be completed in helicopters that involve risk.
In your offshore job, most of the time is spent straight and level in the cruise with the AP engaged with the only risky bits being the arrival and departure at the rig (and these are well prescribed and regulated manoeuvres to maximise passenger safety). It is pretty straightforward to apply rules and regs to such ops because there is little need for dynamic risk assessment whereas those of us whose jobs involve constantly changing scenarios, too many rules and regs get in the way of pragmatic safety and airmanship decisions.