Last two trading days I've noticed SIR SP fluctuations factor in...

Last two trading days I've noticed SIR SP fluctuations factor in a buffer of roughly 8 cents, pretty much most of the day, that has been missing for weeks whilst it just followed the formula of 0.66 x IGO + 52 cents. Maybe when I posted why I was buying up SIR as it seemed no price had been factored in for S2 at all with the fluctuations based on the IGO SP. Interesting volumes through yesterday, looking for upside from here.