I think unless you have some direct, inside information, the sponsorship issue is kept deliberately hazy. First, I presume one and all have signed strict non-disclosure agreements
A lot of streamers can have deep runs here and there but at the same time several I follow are have regular buy-ins of a few thousand dollars with little return. Then the deep runs are often fairly modest in term of prizes as the fields are small. Things do not appear to be covered in terms of making a living (just my perception)
You mention Spraggy and by chance I was just listening to a podcast with Fintan Hand (fellow sponsored streamer) and during the podcast the premise seemed to be they (streamers) play with their own money. Whilst I was not calling it total BS It did not ring true to me and sure enough near the end of the cast, Fintan did talk about PS 'putting' him into tournaments, particularly those with a higher buy-ins.
I think common sense dictates that the sites do not want to sponsor anyone who was struggling to keep their head above water - that would be a dispositive image and poor promotion.
So my
guess would be there might be an equivalent of a per diem involved i.e. sponsored streamers are allowed to play 'x' amount of buy-ins per day.
I used to think it interesting some would be open about their 'balance' and others would never discuss their
bankroll. But then I realized it is easy to fudge a real balance for the sake of the stream (i.e. base it all on 'stream' content) but then the presumption would be they never play a single hand of poker when not streaming?
Of course this is all speculation as the sites are deliberately opaque on the matter. I do not know of any well known streamer/pro who has revealed details of their sponsorship. I presume that is because it is such an advantageous position to be in, even if they lose their sponsorship if they were to reveal details of that agreement it would kill the chances of possibly winning another deal.