@OP
When i tested IP/proxy limits it was clearly looking like instagram limits are IP based. I was trying to run multiple accounts (up to 10) at same time from 1 ip, result were follow blocks. So if you will use too many accounts on 1 proxy you will get follow blocks for sure + maybe pva/email confirmations.
I was also trying to run multiple accounts on 1 proxy in different tools. Here results also were strange. Some bots were able to run 3 accs per proxy, while with other bots accounts asked for PV when i was trying to run 3 per IP.
As i wrote before instagram limits are partially IP based, so its not about how many accounts you run per proxy, its about how many actions in total you perform per proxy per 24 hours.
Good bot + good proxy (residential IPv4 are best but also most expensive) and you can try to run more accounts than 1 per proxy. For example account 1 active only in some hours, account2 active in different hours but i dont advise that. Better optimize your targets, LP, instagram profile etc to get more $$ instead of trying to save some $$ by running multiple accs per proxy.