That's not what they told me some years ago. They said that even though the statement will show the spread margin discount, their risk dept still requires full maintenance margin for both legs 5 mins before the close.
Of course it never made any sense, because they said that when market reopens an hour later, it is back to day-trading margins during new 6PM session.
I gave up on trying to figure out the why of it all, and unfortunately that decision to always trade with full margin all the time has caused me to lose a great deal of money.