Is there a general rule about rating differential for productive coaching?

I understand that 'doing' and 'explaining' are different things and that people who learn very young usually are not good at the latter (since they tend to be more intuitive and less verbally analytical)

- Still, with those and many more qualifiers admitted I'm just wondering if there is folklore about how much better someone should be to be useful as a coach.

(The motivation is that my local club gets requests for more chess coaches than there are available but we likely have a supply of experienced players who are retired from work and may welcome something to do. I'm not there yet but hope to be some day myself.)
- Thanks for indulging my odd curiosity, Bill

-ps- A related question is how much better is 'best' to learn from getting beat by someone. Myself I find about 200 ELO good for that.

I think that there's four factors in a coach:

Rating
Understanding of chess
Ability to teach
Patience

You want all of those to be as high as possible :P

What frustrates me most is losing to players with a much lower rating. So I actually prefer coaches who are lower rated than me so I can gain insights into their type of thinking.

I would say 200 elo is the bare minimum for someone to teach you something but it's not enough, 400 would start to get comfortable.

There is always exceptions for instance prodigious kids could still learn a lot from someone lower rated, that can still teach about certain openings, plans and ways to train oneself.

imo for learning purposes, the higher the player, the better.

they will recognize opportunities and punish you, giving you a chance to quickly learn from mistakes without relying on the computer. for me computer analysis is always a double-edged sword, because sooner or later i grow so interested in how the computer lines work out that i tend to "spoil" many future positions.

in general i think its a logical fallacy that people who are 2x better than you are better at explaining than people who are 50x or 100x better than you. ofc they are on an astronomical level compared to you, but it doesnt mean that they cant explain stuff to you that is simple and basic for them. good examples: Wesley So, Daniel Naroditsky. Very good explainers. Especially So is shocking, as he only speaks rudimentary English, but hes able to use such direct and easy to understand language that its often an eye-opener.
Negative examples:
- Hikaru: "juicer" could mean advanced pawn, passed pawn, any good piece
- Rozman: talks way too fast and scrambles his own thought process by trying to add catchy, impressive and exaggerating youth slang at every opportunity