I later learned that in addition to changing the mentioned sys_property, the data source in the UI Builder config for the "Preview( AI Search Preview UI)" page also contains a gliderecord max number of records. I also needed to adjust this value to match my updated sys_property.

 

In my screenshot below, you see that there is a limit applied on the data source's GlideRecord query in addition to the default glide.graphql.gliderecord.maxResults.limit of 1000. 

 

My updated sys_property: 

 

Confirmation after changing both values: