Why the zerodha/tradesmartonline blocks more margin?

I have checked using span calculator and found that they will block more margin than the loss expected. Why?

Suppose for xyz stock, I buy 1480CE 1000 quantity And sell 1460CE 1000 quantity, in this case the maximum loss for me will be 20k rupees but they are blocking 2 lakh rupees.
I don't understand. Someone please explain.