I use Brain Workshop on desktop and Dual N-Back (by Mikko Tyrskeranta) on Android. But I really only use the desktop app at home since I believe that, like meditation, it's best to do Dual N-Back at a quiet place where you aren't likely to be distracted (and that's home for me). The Android app is only for those really boring commutes.
You're not chunking, because you are not finding a pattern in each set of three.
The strategy you could be using is rehearsal. Are you rapidly repeating the last set of three in your mind, or does it just sit there until you access it in the next comparison? If you repeat it rapidly, you're rehearsing. That's bad (really not the worst though). If it just sits there until the next comparison, you're not rehearsing, good.
Unless there is another "cheating" strategy I don't know about, you're fine. I do the same thing (currently on n=3).
​
Strategies: http://brainscale.net/blog/n-back/the-perfect-n-back-training/82.
THIS is the best one of all that I've ever seen. By far. It let's you do anything from single to quadruple n-back from 1- to 100 n-back. It let's you individualize your game. Make it harder. Make it easier. And if you stick to the normal settings you'll have the scoreboards: Comparing yourself against other n-backers for every single n-back variation (singe, dual...). Competing in n-backing is such a great motivation!
​
https://play.google.com/store/apps/details?id=science.eal.n_backmemorytraining
I'm using this android app: https://play.google.com/store/apps/details?id=cz.wie.p.nback&hl=en_US
Even though the studies usually use a vocal and a spacial stimuli, form and colour do afaik (though take it with a grain of salt as Im not educated on the matter) not work any less than sound. Atleast in the app I have you can freely choose between a single or combination out of sound, position, number and colour.
I didn't know David Asprey. His diet sounds questionable to me, why fats of all things? Isn't a diet rich in fats gonna lead to plaque build-up and countless microinfarcts in the brain?
To n-back. À session takes around 20 min. Also headache after a session is normal. A good way to start is to look at the most common error pointed out in the quote of one of the Jaeggi who's known as the scientist that drew public attention onto the connection between n-back and working memory :
https://reddit.com/r/DualnBack/comments/3wm8et/how_do_you_remember_signals/d1ehucn?context=3