I agree with terri in that the device is not putting out enough voltage for that coil to vaporize the amount of liquid that is being wicked up by the wick. I think it is possible that the culprit is actually the coil heads and not the device, though. If the coil heads you have are not wicked well enough in the factory, which is very common for chinese coil heads, they could be wicking up too much juice and the voltage applied to them is not sufficient enough to vaporize it all, causing a bit of flooding and therefore some spitting. In other words, it may be that the mod is working properly but the coils (rather the poor wicking in them) are the culprit.
It very well could be that a 1.2 ohm coil might be better, but not because it's 1.2 ohm, rather because they may not be defective and are wicked properly for that device. But even another pack of 0.6 ohm coils bought at another retailer could even work better. One just never knows.
This is one of those times where a device that allows the user to adjust the wattage (or voltage) proves to be better over one that doesn't (I don't own any of the latter - I see too much value in full control of my vape). If the wattage was adjustable, you could possibly have been able to up the wattage a bit and solve the issue that way. But since you can't you are at the mercy of the mod and the quality control of the coils.