ORIGINAL: adam_one

Dick,
I understand that you've performed lot of measurements with your test stand, but I wonder whether you've interpreted them right.

Thrust is only a force that is part of the prop's output Power equation, the other part is how much the air is accelerated by the prop, which may be simplified by referring to the prop's Pitch speed as follows:

Prop's output Power = Constant * Thrust * Pitch speed.

Different props (even belonging to the same mfr) have different Constants, which depend on the shape, area and profile of their blades as well as how flexible they are.

Further, props with P/D ratio equal or higher than 0.6 will stall at static condition (as when using your test stand) resulting in erroneous thrust results.
Props with high P/D ratio become inefficient at low forward speed, as when during the take-off and/or climbing. These props also unload much less the motor in flight than props with low P/D ratio.

The power goes to produce thrust AND to accelerate the air (apart from the losses).

So, a prop with a large diameter doesn't need to accelerate the air as much as a prop with a smaller diameter to produce the same thrust.