Shifty - try a search on pprune for urban myths debunked - a thread by Nick Lappos. One of the issues covered was that of ground effect and the myth of the 'bubble' of high pressure air under the disc reducing the IF when close to the ground.
The actual explanation isn't really any clearer since it involves the statement that the proximity of the ground affects the angle of the IF above the disc in such a way as to affect the power required.
AFAIK there is no explanation that doesn't involve pages of maths - perhaps that is why the 'bubble' explanation was so popular - it explained what happened in an easily understood way. Now it is just a question of 'it happens - but we're really not sure why'.
Your manuals seem to obfuscate the issue with such statements as AoA is the same in an IGE and OGE hover which may or may not be strictly true.
However, with reference to your diagrams, if the pitch angle stays the same but the AoA is increased (by reducing IF somehow) then the relative airflow is now coming from a greater angle to the blade which will tilt the lift vector forwards and increase it. Then the drag will increase appropriately and the total reaction will show more lift in the vertical axis and less drag (so less Tq required) in the horizontal axis.
We know we require less power in the IGE hover - that can be demonstrated easily - the mystery is to explain exactly why if there is no pressure increase under the disk.