Additional to those experts “per base” you have some “management”, that applies to your whole company.
First possibility: same mechanism as per base, you have max. 6 experts, they give similar additional bonus… (e.g. 5 experts for agri in your company, one base has also 5 agri experts, that gives +28.4% for global, +28.4% for local)
Second possibility: A little different, maybe more interesting (?): Lets say you have three (?) slots for “management experts” (not per base, but for your company). You could think of everything like them beeing for hire from market, having required “levels” (depending on your max. tier building), having daily costs (salary), giving unique bonuses ("+10% on FP-output", “+50% on EXT efficiency for ALO”,…), number and “strength” depending on the level? They could also “develop” and level up, if you fire them, they go to the market…