My farming experience:
Setup: level 119 (right at the end of the first game run, dlc included) vordt great mace, 427 discovery.
Run description: run mid stairs, use coin, perseverance through the spear charge and kill, the next ones I can go in first no problem, kill the sword one and then kill the red eyed one, go back to the bonfire, repeat
During all the farming I had the covenant item equipped to do pvp online
Results, I think single value that reflects how much time I spent on this is, before the farming I didn't had any large titanite stored, at the end there were 251.
I'd say the red eye knight dropped most of the "proofs" but by small margin.
Around half of them came from doing online, although much like the drops, online could happen and then an hour could go by without happening again. Online wise, I'm not really good or anything, around half of the times I died, but, most of the drops I got them just because right after showing up as a summon someone else had taken care of the business and I was already going back
And I though killing midir would take time... little did I know