Thanks for the info
I went to the
Steam Engine coil calculator and input the numbers for your two setups. I got 8/9 wraps for each of the duals and 5/6 for the single. Heat flux is the amount of heat delivered per square mm of coil surface area. If that gets too low the coil will not get hot enough to make a good vape.
Your single coil = 113 @ 12 watts.
Dual coil setup = 80 @ 16 watts.
I used 3.8v for both.
IMO 80 is too low to get the coil temperatures high enough to make a good vape. You could try to close down the air holes and take slower drags to let the coils heat up more and see if that helps. Also, I would keep all of the outside of the coils clear of cotton. I'm not sure from the pictures, but it's possible you have cotton under the coils. Anywhere that happens you have lost that part of the coil for vapor production.
I also suspect it takes a long time for both of these setups to heat up, the dual being worse.
So, if you like the way the single coil setup vapes, stick with that. If you want to get more productivity from the dual coil, work the calculator. If you drop the resistance to say 0.7 ohms you've gone up to around 20 watts combined, so 10 watts per coil. I bet you will see a significant improvement there. If you put in two 1.2 ohm coils, making it 0.6 ohms combined, you'll have the same performance from each coil as you get in the single setup now so you should get double the vapor production.
0.6 ohms draws 7 amps from the battery at 4.2v, so your batteries will be just fine.
The other approach is to use thinner (higher gauge) wire at the same resistance. That will make coils with less surface area allowing an increase of coil temperature. Again, the calculator is your friend here