How to influence the current-menu-item on single post ?

i started here ( https://kriesi.at/support/topic/single-post-but-on-menu-there-is-a-site-marked-as-active/ ) a topic but i think the header is not sinificant enought – so here a new start :

If i have set a site to be the blogpage site on Enfold Options Page – every single post will be highlighted on main nav that page.
Is it possible to set for e.g. a category which Main Nav Item is highlighted?