Mythbusters found it makes virtually no difference, and lid down can actually make particles go further due to the pressure forcing them through a smaller gap.
Myth Busters are not a solid scientific source. I discussed the issue a bit, linking to some papers in another comment here:
https://feddit.de/comment/5298414
If you don’t shut the lid before you flush it sends poopoo peee particles flying around the bathroom onto your toothbrush
Mythbusters found it makes virtually no difference, and lid down can actually make particles go further due to the pressure forcing them through a smaller gap.
Myth Busters are not a solid scientific source. I discussed the issue a bit, linking to some papers in another comment here: https://feddit.de/comment/5298414