Currently core use config like this one for vless clients:

{"id":"d8e8929b-8b16-4a9f-bf92-d09e1da1e58c","email":"ANVkftyqe8vKxV00hJrkWQo","flow":"xtls-rprx-vision"}

But I suggest add option for default values:

"clients":[{"id":"6c839690-405d-47c4-81dd-7367dc779227","email":"administrator"}...]
"clientsDefaults": {
"flow": "xtls-rprx-vision"
}

This simple solution reduce config.json size from 42.1 mb to 31.5 mb.

And, if we wanna add specific flow or any other parameters in future, we can set it inside client. I mean, using logic like: if present or else