It's understandable to have higher margins but they were hiked even before during no volatility. When we barely have 2 to 1 leverage in midcap equities with many at 1.5 to 1, that is beyond careful.
I understand your point, but you have to keep in mind that earnings season for Q1 is kicking in and with the current situation, there is always a high chance that companies not only largely miss Q1 already downward revised forecasts but also to guide much lower. A down gap of 30% (Conservatively speaking) for a mid-cap stock might not seem like a rare event happening.
Unfortunately you won't be able to convince IB to look at your portfolio basket as a whole (Both Longs and Shorts) and honor the multiple statistical correlations they might have, so having a near neutral portfolio of stocks at this time is not expected to help your margin with IB. Even those statistical correlations might not be honored or respected by the market at times of high volatility & chaotic trading.