Is the so called “free cash”, which is basically equal to amount required to make the strategy in zerodha (bye bye returns!) also required in angel broking, or things make more sense there?
Not understood, can you explain a bit more?
??? 
Zerodha reqires twice the margin mandated by sebi, on wed and Thursday.
The margin requirement for all stock Futures and options contracts will be increased 2 days prior to expiry (Wednesday and Thursday of the expiry week) to twice of the exchange mandated SPAN + Exposure margin required.
They call it “free cash” the extra amount yiu need to keep free if you want ti make a weekly strangle.
I hope you got the point.