ISDT C4 Evo experiences, fan noise.

There is something I don’t understand with this charger - I was trying to “analyze” (test capacity) Vapcel F15 cells, nominal capacity is 1500mAh. I have two cells.

Charger shows cell #1: 931mAh at 0.3A discharge to 2.5V 3h:13m:55s;
cell #2: 959mah at 0.3A discharge to 2.5V 3h:21m:55
So calculations are about right ->>> 0.3*3.2319h = 970mAh, but that’s way below nominal capacity. And this is with manufacturer recommended discharge conditions (discharge 0.2C = 300mA, 2.5V cut off)
I made a second test, I charged cells with BT-C3100, thinking maybe C4 Evo undercharges them. Same results: 924mah and 964mah.

Same cells on the BT-C3100 show 1383mAh and 1390mAh with 500mA charge and 500mA discharge to 2.8V
Same cells on Vapcell BL4 show 1576mAh at 0.5A to 2.5V 3hXXm; 1566mAh at 0.5A to 2.5V 3:08h
How could this be?