Need help with Portfolio Margin in Interactive Brokers.

Hi community,

Can anyone tell me how to effectively use Portfolio Margin in IBKR for long-only ETF portfolio? Is it any different from the Reg-T rule-based model if the portfolio is a simple mix of long-only broad based ETFs and no hedging/options etc are used?

Their website mentions general rules like the +/- percentage bands for individual stocks/etfs and stress test at ~10 points in real-time using general risk-based model. Though we can see initial & maintenance margin in paper account, I cant find a way to figure out how the margin changes when the underlying changes.

In Reg-T we can take 10% loan on long-SPY etf and still be safe because it requires ~87% drop to get a margin call. Whereas in Portfolio Margin model, there is no way to tell how much drop would initiate a margin call. Now this is just for a single etf SPY. My long-only portfolio would have a combination of various broad-market etfs like SPY/QQQ/Reits/Emerging market/Long-term bonds etc. This adds even more complexity to Portfolio Margin. How do I judge how much margin can I take assuming theres a Covid like crash in future and still be very safe from getting margin call?

Any help would be greatly appreciated.
Thank you