Shadow orcs sieges are to soon

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So I have killed only 1 shadow orc which was narrative one (so it seams) at some point even before Khaza Dum bridge location and never encountered then sins than in the wild but I get all out Shadow orcs sieges. This is just savage :)
And this is in a situation where it seams that sieges overall are more frequent in the second part of the game to the point where it is just annoying - getting one with Shadow orcs is just infuriating.