Try your stainless tips as well, IMO, its a little easier to get set up, especially if you haven't fiddled with screen distance. Heres some pics of what I just got from a dirty (40+ uses), 18mm NonG (and 14 works just as well).
I overpacked this, so it's not as even as it usually is, but it's still enough that I wouldn't re-vape it but just save it as ABV for re-processing.
For me, even with no VVPS, this unit is getting 90-95% usually of the actives that can be taken as visible vapor for me in ONE hit with the stainless tip stems. I love it, stirring makes me feel like I'm wasting my life. I just want to rip, dump ABV, and move on. Neither Nano, nor firewood 3, work as well in this regard for me (at present).
(ignore mess off to sides, it's from another vape/session).
This is an uneven grind, over-packed (in air restriction and volume), and probably about as bad as efficiency gets, and about as bad as char gets (not that I mind at this time of night). When done "right" its more even medium to dark brown across the material, with just a few tips of material getting black. This is after about two weeks of messing with the SS tip stems. No VVPS, no dimmer, w/ extension cord (just to save the main power bricks wire). Tried with 3 strains, all similar results ABV wise, cloud wise is another story. On the topic of clouds, it's sort of counter intuitive, but less is more to a point: that point is when it starts restricting airflow.
I use the stem as a straw usually, and take about 1/2 of what I think I'll need, then as I continue to inhale, looking at the ceiling and flipping the stem up. As I'm doing this I'm checking air flow. Then I check visually to make sure not too much is higher than the lip of the SS tip. After this let it heat soak for 10-45 sec, then inhale through water piece at a "medium" rate.
I recently got a firewood 3, I'm still dialing in technique there, and I could not get ABV dark than this: (NOTE AGAIN: NOT UD ABV)
My nano is out with Andy so no shots of ABV right now. I barely use my glass stems for my UD because the 1-hit nature of the SS stems is so convenient for frequent medicating.
Peace, hope you get this worked out!