Effect of helmets and other impressions of the bike rider on driver behaviour? Are there any studies on the effect of helmets and/or other impressions of the bike rider, on driver behaviour?

Has anyone collected their own data on things like this?

Has anyone noticed any other slightly unexpected oddities like the two I observed bellow?

Recently I had to ride back home on a road down a 10km route which I've travelled many times before, but without a helmet, the difference in driver behaviour was very noticeable... I got a lot more space, didn't have a single car overtake me dangerously close (though a few were certainly still illegally close).

I've noticed similar differences when i'm sort of practising riding skinnies by staying dead in the middle of the lines at the sides of roads (this seems to give drivers FAR too much confidence to act dangerously... I was already worried about this particular test after just one day, I was actually interested in getting hard data riding on the lines vs normally vs unstable and wobbly (against number of cars coming dangerously close (based on video)) unfortunately i only got as far as anecdotal evidence that skinny practice on road lines is dangerous as hell, that normal riding seems much safer and that wobbling about unstably does seem to make you safer from drivers, but it's easy to get carried away. Then as I was practicing skinnies some twatwaffle hit me with his wing mirror, putting me off balance, scaring the shit out of me, and ending my desire to gather data, while increasing my desire to keep away from asphalt in general.

Those experiments ended, and I never thought about it much till the helmet incident recently... I'm certainly not intending to do the no helmet experiment myself, so I was wondering is there any real data for this kind of thing, or any other interesting phenomenons to do with driver and cyclist etc?
Seems there are studies showing both:

2008 Walker study - "Cars get closer to cyclists wearing helmets"


https://www.scientificamerican.com/article/strange-but-true-helmets-attract-cars-to-cyclists/
http://news.bbc.co.uk/2/hi/uk_news/england/somerset/5334208.stm
https://www.sciencedirect.com/science/article/pii/S0001457506001540



  when Walker wore a helmet drivers typically drove an average of 3.35 inches closer to his bike than when his noggin wasn't covered.


However in https://helmets.org/walkerstudy.htm  in 2013  this was refuted.  Also https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3783373/


  After re-analysis of Walker's data (2006), helmet wearing is not associated with close motor vehicle passing. The results, however, highlight other more important factors that may inform effective bicycle safety strategies. 




I don't have my own data, merely subjective anectodes about how much room I receive when riding a tandem, or towing a 2-wheel trailer, or the two times I trialled a recumbent and had cars crossing the road to go around me. I'm NOT that wide.

Locally, milk tanker drivers are awesome at passing with extreme room. They don't slow down from their permitted maximum of 90 km/h but they will give me a full lane of passing space where possible, which is 5-6 metres.