FET is not driver. You can not compare currents measured with different setups.
Also, you need to check this: LED test / review - Nichia Optisolis 3000 / 5000 K - ultra high light quality, even with high performance in mid-power class
In few words, you cant get more than 6amps from 4 leds (even without driver) if you use single cell. And big lumen drop while battery is discharging.