I've been growing out my hair and right now its pretty short but still long enough that i can pass for androgynous if im all dressed up with make-up as well. However, before when my hair was like "lesbian" (and i say lesbian because it looked more like a butch woman cut rather than a short male cut because of how i would "try" to style it) short I wouldn't pass even joking, so i would have to wear a wig like the one in my profile pic. I don't have to wear one anymore, though the wig does make me more passable, I honestly have no issue being minimally passable for now.
right now its about mouth-length and I seem to be hit & miss when it comes to passing

but its better than not passing at all xD
The relation between hair and passing depends on more than just your hair length, it has to do with your facial structure as well. Long hair kind of does things to your features that short hair cant. Honestly, your head hair can make a huge difference in the way your face looks regardless of gender. Back when i was male, a simple comb-over meant the difference between looking like a bum and looking like a business man

even if i hadn't shaved.
Hell, even your EYEBROW hair can make a huge difference in your face. Honestly, since waxing my eyebrows to a more feminine style, I pass even better than before and I ditched the wig xD, sometimes less is more.
Also, that Main and Tail shampoo is all myth. I used it for a long time and it honestly made no difference in terms of length or growth, that's all just a marketing tool and has nothing more than a placebo effect. I mean it leaves your hair nice and soft and voluminous, but it doesn't speed growth. If you want your hair to grow faster, take fish oil supplements, hair/skin/nails supplements, or eat more salmon. All those things increase the speed at which your hair grows. But not drastically