I've recently asked this question on Math SE and upon not receiving any answers, offered a bounty to draw attention. The question has attracted a reasonable number of up and no down-votes, so I'd say its as "good" question, according to the guideline.
As no answers have been posted, the bounty has expired. My question is if it might now be sensible to migrate this question to MathOverflow (and if not, why), as I expect the possibility of someone posting an answer to be higher, even though I am just a maths student, not a professional, by any means.