basic long/short carrying cost question

[silveredge]

T+2. If you're assigned on a Friday expiry you receive the cash on Tuesday.

When I am long 100 shares, short 1 call at K1, short another call at K2. Which of the calls is considered naked short for margin?

 

[elt894]

When I am long 100 shares, short 1 call at K1, short another call at K2. Which of the calls is considered naked short for margin?

I'm not too familiar with RegT margin rules, but I think I remember reading on IB's website that they don't guarantee that positions will be grouped in a way that minimizes margin. I recall some posts where buying a call caused a low-margin spread to be regrouped and resulted in a large margin increase.