Because the devices use a radio broadcast communications system, they do not have to be in visual line of sight of each other; however, a wireless path must be viable.
Since it is the main that chooses which follower to address, whereas a follower is in theory supposed to listen in each receive slot, being a main is a lighter burden than being a follower.
A cleric named Poppa, perhaps the same one, also appears in Adam of Bremen's history, but in connection with , who had supposedly conquered Denmark the fact that Eric conquered Denmark during the realm of Sweyn Forkbeard is explained by Saxo as a punishment of Sweyn's.