Interesting power test on K40

I have done a number of tests with quite interesting results.

It looks like 70% (11 mA) is the most efficient output my laser tube provides. Although power increases from 11 mA to 16 mA, it does not cut deeper.

I am surprised that from 20% to 30% there is only 0.5 mA more power but 3 mA from 10% to 20%

The test is done at 2 x 3.33 mm / sec and with a water temperature of 20.5 degrees Celsius.
The acrylic piece itself is 14.5 mm deep.