To make my recommendations more clear:
If I use the precise algorithm alone I get less than 1 % false pairs at a threshold of 70 %.
If I use the standard algorithm ("content") at a threshold of about 90 % additionally, I get a few percent additional pairs (with a "precise" rating close to 0), but with a higher false pair probability.
I don't trust in auto-marking, I just use it as "click-saver".