Being of a somewhat masochistic bent, I just finished HK for the 35th time. I will not buy him... I can say that, the low statistical significance of 35 samples taken into consideration, I have most often found the part along the wall to the left when you enter. From the first group of enemies and to the tents on the other side of the rotunda. O fcourse, there have been a couple of strays, in the centre and elsewhere, but usually in that area. Good Luck!
And announce that you're scanning, often there will be others as mentioned above.