honestly, the promote feature of steemit is being used very less, especially for the private accounts which are not backed up by large investors or companies.
What I would suggest the best option for you, is to "promote" your posts either through biding bots (e.g. booster, postpromoter, smartsteem) or through voting bots (e.g. minnowbooster or smartmarket). The main reason why this is being used is, that the amount you spend is given back to you through votes.
The best website to see all the voting bots is: https://steembottracker.com/
I hope this helps you aswell, even if I could not find the direct answer to your question.
Greetings @bitcoinbarometer