And, as long as we're making suggestions, BookFunnel. I've noticed the promos I participate in there tend to have a larger number of authors than those on Prolific Works and Story Origin, as well as more activity. (At least for me; I know people get different results. Results may also vary by genre. The number of authors may sometimes be affected by how specific the requirements are, since sometimes sponsors cast a very wide net; other times, the range of permitted books is extremely narrow.)
Current BookFunnel Newsletter promo: authors: 112, book claims: 142. (science fiction and fantasy)
Current Prolific Works Newsletter promo: authors: 32, book claims: 8. (science fiction and fantasy, stories about portals to other worlds only, hence more restricted possibilities for authors)
Last Month's Prolific Works Newsletter promo (Featured by Prolific Works): authors: 57, book claims: 68 and 47 (two books) (science fiction, fantasy, and horror)
[This is not intended as a put-down of Prolific Works. I'm still going to try future promos there. But if you're experimenting with new approaches and only want to start with one (since there is a cost connected with each one), BF might be the most logical choice.]
The problem with a lot of indies these days is that we're crazed. Those of us who are trying to make a living at it have to keep up with what seems like daily changes in the environment. Those of us who have a day job end up with very limited time to write, let alone promote. I don't think there's anything wrong with your setup, JD. The promos sound like great opportunities. But it may be the days are past when a forum, even a large forum, is going to stir up enough interest by itself. Going into an environment in which authors are actively looking for cross promotion opportunities seems like the best bet under current conditions.