This isn’t an issue specific to Zerodha. An additional 2% margin is being blocked for all short positions irrespective of whether the position is hedged or otherwise. This is as per the recent SEBI circular:
The increase in ELM by 2% is on the entire contract value. So for every lot of nifty option being written (assuming nifty is at 23000, lot size 25), margin will go up by ~12-13k.
Also, from February 01, the margins will rise further since the calendar spread benefit will go away for contracts expiring on a given day. You can read more here - SEBI's new rules for index derivatives: Here's what's changing – Z-Connect by Zerodha