It's easy - the more accounts per proxy, the higher the risk. If you value them and want them to grow a lot - 1:1 ratio is the best. Otherwise, I wouldn't suggest doing more than 5 accounts per proxy. This is because it's the maximum number of accounts allowed per 1 IP, so it wouldn't be smart to stray away from this.
The 5-7 accounts per IP ratio works on mobile proxies because we’re naturally allowed to connect up to 5 accounts on a device. However, if one gets shadowbanned or permanently banned, expect that all connected accounts would have been affected.