Hey Jamie,
You could try raising it a bit, but some dual use while transitioning is fairly normal. Going to two cigs a day is a fantastic start!
Some coughing is normal early on especially dual using, but if you are using a mod with high power outputs and high clouds, even 3 nicotine can be too much for one's throat, early on. When I quit, I started on a DL device (inhale like sucking through a straw, higher wattage) and my throat and lungs couldn't handle it. The coughing (I was using a DL device with 12 nic, way too high, got nic poisoning and it did subside when I lowered my nicotine some, but Dl was still very hard on my throat and lungs.
Since you have COPD, I would suggest a smaller, MTL device with adjustable wattage and airflow to see how you like it. MTL starter kits are pretty inexpensive and you can find tons of recommendations for that, or just start a thread to get recommendations. You can still save your other device for when you want more clouds, or if you enjoy the wide airflow.
In a MTL tank I vape at 15 mg nicotine but since the quantities of vapor is so different, I don't think I'm getting more nic than if I chain-vaped a DL high output delivery tank. I was able to transition then, and it will be useful to try different options to see what you like. Some people starting out have one lower nic device that they use all the time but a tank set up with more nicotine to vape through more of the intense cravings, so even if you prefer your current device, a MTL with more nic might end up being your go to device for cravings!
Best of luck, I can see you are really wanting to make it work, and you will. Things I used to help me besides vaping: Knitting (keeps my hands busy and thoughts off nic when I can't vape, etc.) taking up new hobbies (I'm learning the guitar as I got my voice back and I like to sing) and the support of this site. I got so much invaluable information and support and encouragement here, and I NEEDED that. Some folks don't, but I did, and it kept my thoughts focused on vaping when I wanted to smoke.
But two cigs in a day is HUGE, right? When's the last time you did that?
Anna