Is it the same book that you've run before? Or is it a first run BB? I do see diminishing returns with recurrent promos for the same title.
Personally, I can't say for BB as I've never ran a free there (or been graced with an approval for one).
My reference to 40k was what I normally expected from a BB freebie ten years ago. That is a different topic. The entire industry has changed since 2010. *sad sigh*
I am talking about across the board and not one particular title. And I am not talking about diminishing returns. I get about the same number of downloads for recurrent promos.
What I am talking about is what we all know; that most free downloads are never read. By my observation, about 10% are, which means that when I have a free promo with say 12K downloads (about typical for a BB promo for me) I actually have about 1200 novels that are read. I can expect to have a sell-through of around 1000 novels in whichever series it is. (All of my novels are series titles)
So I have come to the conclusion, or just about done so, that I may as well do 99¢ promos. In fact, I am growing reluctant to even do a free promo. Of course, 99¢ BB promos are harder to score, but I might settle for stacked promos with smaller advertisers and BB ads if I don't score a BB promo.
(I have had maybe 20 BB promos over the years which doesn't mean I can count on them. I sometimes get a bunch in a row or other times go 6 or 9 months not able to run one. 🤷♀️)