A single correct dose is a myth.
The author even sort of notes that with the differences between teenagers, 25 year olds and the elderly.
There's also a wide variety of sleep disorders which are touched on in the article.
I've suffered with 2.5mg before for long enough to understand that it doesn't work for me, no matter how many studies you have with 95% CL that the dose is much lower. The 5mg tablets work much better for me.
If you get results at a lower dose, that's fine, I won't tell you to try using more.
I'm a 49 year old though with moderately severe DSPD and at least used to have non-24 hour disorder and would be happiest letting my schedule shift 1-2 hours every night during college for a few years. If you're a 25 year old and you've never quite had sleep that fucked up which wasn't entirely self-inflicted due to partying then you're not me (most young people who think they have bad sleep disorders are just actively doing things to fuck up their sleep and when they stop doing those things they're magically cured -- and then they turn into the most insufferable assholes because they think they understand sleep disorders when they don't).
And one thing to understand about melatonin is that its not really an anxiolytic and if stress/anxiety is keeping you up it may not work (it will not make the pandemic go away). I also find that I need to take it about an hour before bedtime, and rather than making me tired, it more allows me to get tired. I still need a nighttime ritual to unwind.