Descriptions of Horus vs Images of him.

its 40k it doesn't really need to make much sense.
im sure there is probably enough sensor equipment in his terminator armour to alert him to any presence that maybe behind him and well he is a primarch so hes probably got extra sensory perception or something like that.
now i cant remember of the top of my head, but I'm sure before then he had already been gifted his terminator armour by the fabricator general, so I'm sure he would have started to look like that by then

Angel of Blood said:

Meh, i know what everyone means. But i just just imagine Primarchs as wanting to have a full uncomprimising view of their surroundings without having to rely on sensors no matter how advanced. Hence why none of the other Primarchs of the Emperor himself use Terminator armour. They all wear armour far beyond that of any other soldier, yet none of others wear armour that blocks their view

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well actually perturabo primarch of the iron warriors also wore terminator armour,

http://wh40k.lexicanum.com/wiki/Perturabo
well it doesnt actually say he does, but the artwork does

i think hes on about the fight between them on the ship before the massacre, could be wrong tho

actually been in terminator armour wouldn't really effect the peripheral vision of the wearer as a humans peripheral vision is only 180 degrees so something like this "D" so been in terminator armour wouldnt stop that.
also normal space marines with there enhanced senses can sense an enemy behind them, so if a normal marine can do that imagine how much better a primarch would be.
also been primarchs there armour is vastly superior to regular power and terminator armour

Its going to be pretty much like that for dude in power armour they wont be able to see behind themselves much either, you think with the helmets visors been the way they are and the large power pack.
So i doubt termie armours visual performance is much less then power armour and when you have a primarch in termie armour i can imagine them been nigh unstoppable, they're nigh unstoppable in power armour let alone termie, plus termie seems far more intimidating

exactly, some of the marines in the books iv read have taken their helmet of for exactly that reason

the visors arent irrelevent, they will still restrict peripheral vison somewhat. its like in 300 towards the end where the main dude(always forget hes name) takes of his helmet because it narrows his vision even tho he can perfectly see out of it and can turn his head, its the same kind of thing
and iv already mentioned that each primarchs armour would be vastly superior to reqular power armour