Excess SIPC coverage aggregate limit is only 0.1% of user assets!

I am concerned that IBKR's excess SIPC insurance with Lloyds only covers 150M aggregate, but they have 128B of user funds as of their last annual report. I have way more than 250k of cash on there due to short sales. What % of user funds of a retail broker typically falls under the SIPC thresholds?

 

short sale cash isn’t protected. It’s not your money.