If you have 3 LEDs in series with a 2.2 ohm resistor and the resistor has 0.32V across it Then the current for this string is 0.146A.
You have 4 strings so the total current is 0.58A.
If you are using the 6V battery then the regulator is operating at its dropout limit so it will dropout causing the voltage to drop when the battery voltage drops.
You have 4 strings so the total current is 0.58A.
If you are using the 6V battery then the regulator is operating at its dropout limit so it will dropout causing the voltage to drop when the battery voltage drops.