Just hovering
Mart
The easiest way to get your head round what is happening with an un-autostabilised hovering Harrier at speeds of less than (say) 30 kt is that no significant aerodynamic forces are produced by the wings, tailpane and fin.
This means it is just a hunk of stuff supported by the engine thrust and your piloting task is to keep the aircraft flat (or to be more precise in the same attitude it has on the ground before a VTO) so that the engine thrust stays vertical.
Clearly if you let the roll or pitch attitude change the thrust will develop a component in some direction that is other than vertical and off the aircraft will wander.
I say un-autostabilised because when the first RAF and USMC guys were converted there were no two seaters and no simulator. We chose to convert them autostabs OFF so that there was no chance of them experiencing an autostab hard over failure case. Back in the 60s electromechanical things were not as reliable as they are these days and we saw the slightly twitchier handling with stabs off as very much the lesser of the two evils.
At such low speeds (and without aerodynamics) the aircraft is neutrally stable in roll and pitch. So it does not particularly want to move in those axes however if it is disturbed in the least there is no damping to slow down the motion and certainly no stiffness (stability) to correct the motion. Only the pilot can correct the motion and so restore the attitude by moving the stick instinctively just as if flying normally. This moves the ailerons and tailplane which having no airflow over them achieves nothing. However the aerodynamic surfaces are mechanically linked to the shutters of the appropriate reaction controls so the effect to the pilot is that the ailerons and tailplane work as normal despite there being no airspeed.
Now for two big ‘buts’. Firstly the story in yaw is not so simple. Because the intake momentum drag acts ahead of the CG and increases with RPM it has a big influence in the hover. If the nose is not kept into wind (even 10kts) then the aircraft will yaw and try and fly tail to wind. So in yaw the hovering aircraft is not neutrally stable it is actually UNstable. This requires continual footwork – not terribly difficult to do but you MUST control the heading at all times. You can CHOOSE to have it 90deg to the wind if you want, but you will HAVE to hold it there with your feet.
The second ‘but’ is that although people may not realise it when they fly normally in a fixed wing aircraft they are using ‘rate’ controls. In other words say you put on a bit of aileron, the aircraft starts to accelerate in roll but if you hold the control where you first put it the normal aerodynamic roll damping comes into effect and stops the aircraft continuing to ACCELERATE in roll leaving you with a steady RATE of roll. There being no aerodynamic damping in the hover the reaction controls are pure acceleration controls. In the 1950s there were two schools of though about this. Pilots would over-control if faced with acceleration (vice rate) controls and finish up oscillating. Or they would not!
Hawkers thought pilots would be able to cope so they went ahead on that basis. Others decided that it would be necessary to produce artificial damping and stability to effectively leave the pilot with a rate control system.
Once Hawkers got going it became clear that pilots could adapt to acceleration controls provided a few criteria were met. The control runs must be as low friction as possible with no backlash at all and the forces available from the puffer should be able to produce an acceleration of approx 2 'pie' radians per sec squared. Anything less ‘punchy’ and you tended to get out of phase with any oscillation and struggled to damp it out.
This was especially so in roll where there was very little inertia (if you think about it inertia resists acceleration and so acts as a quasi damping term) Therefore the greater pitch (and yaw) inertia was a help to pilots.
I have not answered some of your points about anhedral etc directly because it is not a factor in the hover only in transition which is another story and this post is too long already.
Hope that helps a bit.
John