I know someone who gets 2664 every month on one ID but not the other.  She gets the free relists on both IDs and she sells a lot more on the ID that gets the 2664 offer.  She has two selling IDs and has never had a store.

She sells for a few months and then takes a month or two off, but so far still gets 2664, so if it drops off due to lack of sales they obviously don't base it on the last month alone.  Last time she listed she hardly sold anything (she reduced a lot of prices to clear stock and usually gets lots of sales when she does that so we think it's due to appalling category changes) so she's wondering whether she'll continue to get 2664 much longer.

One thing she does is always accept extra offers, even if she doesn't plan to use them.  I don't know whether that makes any difference but we both thought that perhaps ebay will stop giving them to us if we don't use some of them.  They could track how many people accept them but never use them, but there's no way we'll ever know.  I'm guilty of not using a lot of the extra freebies, and even of the 40 on one ID, but while my main ID is busy I see no point in pushing myself to list much on the other ID.

I think trying to analyse some of ebay's actions might be a waste of time because they don't seem to be consistent in a lot of things, but I too can't help doing it.