So far, five times expansion and IIRC the number participants never get deduction. The total participants would be 95, which is really high, but it's still not beat the previous biggest campaign which ever accept 115 participants.
If signature campaign aren't working, they won't want to expand for five times.

It is likely that in the coming weeks Rainbet will continue to expand their campaign by adding more participants, making Rainbet the largest campaign by number of participants.

As the exposure of the signature campaign on the forum is high that the expansion is done several times by the manager, as they keep focusing on the signature campaign rather than the contest.