You’re right that 1 account per proxy is the safest, but I get wanting to cut down on proxy costs. From my experience, you can usually run 2-3 Telegram accounts per static proxy without much risk, as long as you don’t have them all doing the same thing or joining the same groups at once.
Once you go over that, like 4-5 or more, the chance of getting flagged or hit with phone verification goes up fast. Hope that helps
If you tell me where you’re posting this (e.g., forum, group), I can tweak the tone!