I'm pretty sure from memory that results from wgContentNamespaces get boosted in the search results, but this doesn't seem to be mentioned anywhere, including in the page weighting section.. Something we might want to add ?
Topic on Help talk:CirrusSearch
This configurable but in general (at least for WMF wikis) wgNamespacesToBeSearchedDefault namespaces are slightly overboosted. Because this is all configurable there are no single and simple answer to this question, it is wiki dependent. I'm not against adding something about that but I'm not sure where.