I did configuration of few predicate to Sites Admin Search Rail and Assets Admin Search Rail. Changes work fine when I am under Location:Assets or Location:Sites in search bar. But these changes are not picked when searching at global level (If I remove Location:Sites or Location:Assets and then search for any page or asset, search form changes are not picked).
I think it is default behaviour of AEM. Only option I see is to customize omni search. Please reply in case faced such scenario or did customization to omni search.