Although I can't seem to access your photos, I would suspect that what you saw (just in front of the rear para doors?) were the IRCM transmitters. They have been discussed previously in open source (Jane's etc).
Apart from some certain areas of the UK, the lowest level for fixed wing ac, including the Herc, is 250 ft MSD meaning that the ground (including valley walls) shouldn't come within a 250 ft bubble around the ac.