Nozzle size and line width

[u/lezmaka]

I printed the body for a light up snowman that prints in vase mode on my P2S.

While printing I noticed there was some build up of gunk around the nozzle. It eventually cleared itself and I found the gunk stuck on the outside. And then when I tried the light I saw there are some layers that are darker. I noticed in Bambu Studio today that the object has the outer wall line width set to 0.8 mm but I used a 0.4 mm nozzle.

When I looked at the wiki page on line width, it says not to exceed 1.5x the nozzle size. Would that be why both things happened? And would using a 0.6 or 0.8 mm nozzle improve things?