FCOB WS2811 24V not fully on

Hello, I have purchased a 5m log FCOB led strip, from here. Specs says that it should have about 14W/m, but I measured only 20W(23.5, 0.8A with a PSU rated at 24W 2.5A) for the whole 5m long strip.
In order to test it I used an Arduino, so the data line was at about 5V, which in my opinion should be enough, because all 60 chips seems to be working. It is planned to be used with a Wemos D1 mini, but not yet arrived, perhaps I have to rise the voltage to 5V.

Does someone else experienced something similar? It is a faulty led strip? Is it the real wattage 20W? Or am I doing something wrong?

Thank you and best regards