There’s another admin setting for max consecutive replies which affects how many times a user can post in a row. Would changing that help in your case?
Why I could not find it is because I did search but missed it, either search “max” to find for exact match phrase, “max replies” was not turning it up for me, “replies” but somehow I missed it.
Set to 0 to override. Seemed to work.
Busy forums trip over this default setting almost instantly.