My sense is that they treat each spread leg as outright, flat price risk which would be incredibly wrong.
I use IB as a back up broker with a small 30K$ account. I am not sure if they apply exact SPAN margins but they definitely don't use 2x outrights or even 1x outright margins. IMO they use just slightly more than exchange SPAN margins.
. Make money if you can. I like trading spreads, particularly CL spreads. Much safer than the outright....