I know the pack says the side of the neck is preferable, but BH always does it above the ribs behind the shoulder - it's MUCH easier to do - in a race, anyways.
And for anyone who hasn't selected their 'system' yet : Heptavac STINGS, Covexin doesn't. (Which means the sheep may jump when you've done them with Heptavac and hardly seem to notice the Covexin.)