By direct experiment you can prove that 0.8mm pressing can NOT form a 0.855 cm of neck as required by 15° arch.

Phew claims such neck can be form by the difference length of [ 3.17157/4 * (15/45) - 0.261 ] * 100 cm = 26.429 - 26.1 = 0.329 cm.

Pressing as far as 0.329 cm for a straight object (ruler) of 26.429 will result a 15° neck of 0.855 cm.

Despite the fact that the shape of the arch formed is not a circle (it's likely a catenary) your measurement is quite in error. We have only your word in capital letters ("NOT") that the ruler will not bend for a 0.8mm pressing. It's actually quite easy to show that only a small shortening of the endpoints (0.8mm) produces a significant bend (0.85cm).

Shortening it by over 3 mm (0.329cm) will easily bend it by about double the 0.85cm.

It's pretty easy, but does require some care in measuring.

As I've pointed out before, you suck at measurement.

But it's a measurement any competent person can reproduce.