All things being equal, you should find that you run the 1.8 coils at lower watts than the 1.6 coils.
Generally, the lower the coil resistance, the higher you will run the watts.
You should get better battery life from higher resistance coils because they use less wattage.
For me, the sweet spot setting is when the coil makes a sound like sizzling bacon and I try for no popping, just sizzle. I don't like liquid popped up on my tongue or lips. It sometimes requires fine tuning volts/watts, tank air flow as well as a consistent draw each hit.
Right now, I have 1.8 Aspire Clapton coils in my Nautilus. The actual resistance of the coils is being read by the mod at 1.75 and the coils are running perfectly for me, the juice I'm using and the way I vape, @ 13.6 watts.
I have drilled out to slightly enlarge the the largest air flow setting on the Nautilus. Without that little bit of extra air, I would likely use just a bit lower wattage to get that same sizzle.