This value sets a max limit on how many objects a given word among several with full text search can be assigned to before it gets ignored, to avoid pointless words like "the" having a significance on the search results. It is currently set to 20 which is way to low.

Instead this should use percentage of number of content objects, in legacy this is set to 60%, it is often seen as being to low for smaller db so can be set to 66% (2/3) by default.

A future improvement on this is to make this configurable, this is covered by EZP-24209.