Your atomizer could be a Nickel 0.15ohm (Ni Temp mode), or the EC 0.3ohm (Normal watts mode). Eleaf do a Nickel 0.5ohm, but I don't think you have that one.
Either way. These are low resistance coils. You need to match the mode to the coil.
18mg liquid is very strong for a coil intended for 30-60w. I'm not fully sure how your mod works, but if you set it the wrong way or try to vape it with a low setting, you will not get much 'vapor' (smoke...)
If you had 6mg liquid (or 3mg) I would suggest using the temp control Nickel coil and see how you go with 25-40 watts/460-500 F. Not all mods work the same though. Some mods reduce the power to 'barely working' if you hit the temp too quickly, then it doesn't matter what you set the watts to, it won't go there.
If I had to guess, I'd say if the mod is reading 0.27ohms, it's probably the Nickel 200 temp coil.