I can now finally conclude, that forced HBAO+ is impossible in ArmA II & Operation Arrowhead without one issue or another. The official "0x00000013" flag causes the grass to look very "fuzzy", and flickers on and off depending on viewing angle and distance. The only two real alternatives to this are "0x00000016" and "0x00000026". The "16" profile is slightly less prone to flickering on and off than "13", but unfortunately bleeds through distant fog. On the other hand does "26" apply a more subtle effect than both "13" and "16", but also flickers on and off especially on grass.