Check any of my posts where I have stated static thrust measurements for my engine / prop combinations. All of these figures I have accurately measured with my test setup. My results have proven to be repeatable, and also correlate with what I experience in the air. They all have shown Thrust HP to be optimistic. The degree varies, but seem to get worse as pitch goes down and diameter goes up.
Here are a few examples:

Mejzlik 20x6 @ 8800 RPM - Measures 20 lbs, 4 oz thrust. THP says 37.17 (used APC airfoil)

Zinger 20x6 @ 8300 - Measures 19 lbs, 14 oz. THP says 31.19.

APC 17x6 @ 9400 - Measures 17 lbs, 12 oz. THP says 22.14.

APC 13x4W @ 11,800 - Measures 8 lbs, 12 oz. TP says 11.93.

You get the picture