Stock
coils are not exactly known to be 100% accurate. If the coil is reading at .56 accurately, it will read .6 on an
istick. (if the iStick is accurate). A small difference (.2) in measurements is nothing to be concerned about. Also as the coil gets used it will gunk up some changing the reading to a slightly higher reading.
The rule for ANY vape device is the same. Start with low power, take a draw and add more power (wattage/voltage), then take another draw. Repeat as necessary. If your vape gets too warm or starts to taste burnt, back it down.
Good luck in your vape journey.