Originally Posted by
SoSmellyAir
And most YouTube videos I have seen recommend a single digit mm distance.
Totally agree. Having set up countless RDs, I'll be even more specific, 5-7mm seems to be the right distance for most RDs. It gets the upper jockey wheel as close as possible to the cassette, without the top of RD cage fouling the cassette as it is shifted into the higher gears.