There are websites like https://liquidity.vision/
that help track your impermanent loss on your current pool positions. Why doesn't zapperfi include this sort of data? Just a quick calculation of initial balance of tokens compared to current balance of tokens.
Keep it simple; only measure IL from the latest position (after any liquidity additions/removals) to avoid any sort of confusing averaging of cost.
Adopt the assumption rule that liquidity vision does where it still shows your positions after staking your pool tokens. Easy to assume; if pool tokens are sent to a smart contract instead of removing liquidity, assume the tokens are still under the user's possession. Add an * to the UI to communicate the assumption in the dashboard.