Realy? If I make 6 different sizes - that must work!
K2 very good comp. but if I have a lot of articles - that is very difficult and long add images via admin(((
Maybe anybody help how he doing that work quickly?

Since you insist to hack core K2 files the code that is generating the images is located at /administrator/components/com_k2/models/item.php line 270. Note that you will lose your changes in future K2 updates.