After having my CIs for 4 (Left) and 6 (Right) years and talking with a lot of CI users, the only response I know to give is that no ones / ear situation is "normal".
I am Bilateral and each of my ears is different in how the controller is programmed / mapped. Each ear hears good on their own. My left ear is "better" than my right in that I can understand speech a little better and seam to favor it more. The Left ear hears the speech frequencies easier and it is a little clearer. My right hears some other frequencies better. Together, both ears allow me to interpret sound quite well given that without them, my hearing ability is non existent.
So wondering about your situation and some questions you can ask the audiologist:
Why are the 8 electrodes shut off? Get a reason and not one like "that is what we just do" I'm sure there is a reason. These audiologists are pretty good and from what I know, they have received quite a bit of training.
Is it that you feel the electrical stimulation on those 8 and it is better when they are turned off? How about turning the C levels down but still use them.
Are you able to nail down "Which" electrode or range is giving you the stimulation still or is it that when you are being mapped, you don't feel the stimulation but when they turn on all electrodes, you then feel it?
For me, I noticed this at one point during my adapting to the CIs. I told the audi about this and we pushed each electrode further to figure out which ones (18 and 19) were contributing to it and adjusted them down a little. Sensation relieved. But that is my story.
You mention pressure and burning. I'm no Dr but have pushed my maps pretty extensively. Couple ideas to ponder. Have you thought about removing the magnet from the coil and using a head ban to keep the coil in place just to make sure the magnet is not to strong and putting pressure on the implant area. This could also isolate the magnet vs coil electrical activity?
The pressure may be related to the electrical stimulation of the nerves. I can't tell you what to do but if it was me, I would try turning down the volume AND sensitivity on the processor to see if that helps. For me, when I run the sensitivity high and volume slightly increased, there are certain frequencies in some environments that set off a "feeling" that I have learned relates to a little to much stimulation and I turn down the volume and sensitivity and it gets better.
Hope your able to find a happy medium.
I hope even with the draw backs, your choice to get an implant was a good one for you.
For me, I will never look back.
Steve