The upper horde:
see page 24, treatment of hills - as the LP is behind the hill, the terrain piece cannot be ignored, so the unit does not have LOS to the regiment
The bottom regiment:
page 25, drawing LOS, the second paragraph - the upper horde is partially “inside” the hill, so the regiment can draw a LOS to the unit
I am not sure if this is a topic where 3ed rules should be discussed but that’s another matter. 
EDIT: In a way, I agree with @MiSiO_1 that the interaction of units with hills is a bit confusing. I have my own issue with it related to providing cover. I posted about the matter in this topic, Hills and cover in 3ed. I do not think I got a good answer there then. 